Display device, method of manufacturing display device and electronic apparatus

ABSTRACT

A display device comprises a microcapsule-containing layer including a plurality of microcapsules. A variation of the outer diameters of the microcapsules can be defined by an average value and a CV value. Each of the microcapsules is comprised of: a shell having an inner surface; contact particles electrically charged and provided within the shell in an contact state that the contact particles are in contact with the inner surface of the shell; and a scattering body for scattering light; or a colored particles having a different hue from the hue of the contact particles. The display device further comprises a pair of electrodes that when an electrical voltage is applied to between the pair of electrodes, electrical fields to act on the contact particles are generated. The average value of the outer diameters of the microcapsules is in the range of 20 to 60 μm, and the CV value of the outer diameters of the microcapsules is 20% or less. In a case where the electrical voltage is applied to between the pair of electrodes, the contact particles are moved along the inner surface of the shell while maintaining the contact state with the inner surface of the shell.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims a priority to Japanese Patent Application No.2008-272548 filed on Oct. 22, 2008 which is hereby expresslyincorporated by reference herein in its entirety.

BACKGROUND

1. Technical Field

The present invention relates to a display device, a method ofmanufacturing a display device and an electronic apparatus, and morespecifically relates to a display device, a method of manufacturing thedisplay device and an electronic apparatus provided with the displaydevice.

2. Related Art

It is generally known that, if electrical fields are allowed to act on adispersion system in which fine particles are dispersed in a liquid, thefine particles move (or migrate) in the liquid by a Coulomb force (anelectrostatic force). This phenomenon is referred to as electrophoresis.In recent years, an electrophoretic display device that displays desiredinformation (images) using the electrophoresis draws attention as a newdisplay device.

This electrophoretic display device enjoys reduced power consumption,because it has a display memory property with which a display content ismaintained even at the time of stoppage of voltage application. Inparticular, since the electrophoretic display device performs itsdisplay operations using reflected light just like general printedmatters, it has such features as a broad viewing angle property and ahigh-contrast display capability.

As one example of conventional electrophoretic display devices, JapanesePatent No. 800963 discloses an electrophoretic display device that makesuse of an electrophoretic dispersion liquid prepared by dispersing twokinds of electrophoretic particles charged with opposite polarities toeach other in a liquid phase dispersion medium.

Further, Japanese Patent No. 2551783 discloses an electrophoreticdisplay device that makes use of microcapsules, each of which includesan electrophoretic dispersion liquid prepared by dispersing one kind ofelectrophoretic particles in a liquid-phase dispersion medium, and ashell into which the electrophoretic dispersion liquid is encapsulated.

Furthermore, there has been proposed a combination of the twoelectrophoretic display devices disclosed in these patent documents,i.e., an electrophoretic display device that makes use of microcapsules,each of which includes an electrophoretic dispersion liquid prepared bydispersing electrophoretic particles for white color display (whiteparticles) and electrophoretic particles for black color display (blackparticles) in a liquid-phase dispersion medium, the white particles andthe black particles being charged with opposite polarities to eachother, and a shell into which the electrophoretic dispersion liquid isencapsulated.

In the conventional electrophoretic display devices, an absolute valueof a net charge amount of an inner wall of a retention wall(partitioning wall) or a capsule (the shell) is smaller than an absolutevalue of a net charge amount of a surface of each of the electrophoreticparticles, and charge polarities thereof are opposite to each other.

As a result, if electrical fields act on the electrophoretic particles,they are moved parallel to an application direction of the electricalfields toward an electrode having a charge polarity opposite to thecharge polarity of the surfaces of the electrophoretic particles.

With the conventional electrophoretic display devices, a difference inelectrophoretic mobility or the like between the electrophoreticparticles (the white and black particles) is used in obtaining a graycolor of specified gradation which is an intermediate tone (intermediatecolor) of white color and black color.

A specified magnitude of the electrical voltage is applied to between apair of electrodes for a predetermined time in such a fashion that aperfectly white state is not changed to a perfectly black state or aperfectly black state is not changed to a perfectly white state.

This creates a state that the white particles and the black particlesare dispersed or aggregated in a specific region in the liquid-phasedispersion medium. Thus, the gray color is obtained at any rate.

In the conventional electrophoretic display devices, however, it isdifficult to obtain a specific intermediate tone of a gray color orother colors of specified gradation.

More specifically, if the electrical voltage is applied to between apair of electrodes in a perfectly white state or a perfectly blackstate, the white particles and the black particles are moved from oneelectrode to the other electrode in a liquid-phase dispersion mediumwhile colliding with each other, respectively.

Further, when the gray color is displayed, the white particles and theblack particles exist in a mixed state. This leads to inferiorreproducibility and makes it very difficult to obtain a gray color ofspecified gradation.

Even if the gray color is obtained by stoppage of the application of theelectrical voltage to between the pair of electrodes, such a state isunstable and is changed over time.

In other words, since the white particles and the black particles arefloating in the liquid-phase dispersion medium, they are moved in theliquid-phase dispersion medium over time. Furthermore, since the whiteparticles and the black particles are electrically charged with theopposite polarities to each other, they are adsorbed together so that aplurality of the white and black particles are aggregated together.

For these reasons, even if the gray color of the specified gradation isobtained, the gray color cannot be maintained as it is and thus adisplayed image becomes highly unstable.

Moreover, the mutually adsorbed white and black particles need to beseparated prior to providing the next display. To this end, anelectrical voltage having higher magnitude is repeatedly applied tobetween the pair of electrodes while alternately changing its polarity.Otherwise, an additional electrode needs to be provided for thatpurpose.

This makes a control operation and a structure of the conventionalelectrophoretic display device complicated, and leads to increased powerconsumption thereof.

SUMMARY

As a result of keen examination, the present inventors have succeeded infinding out a method (an electro-crawling method) by which electricallycharging contact particles (fine particles) are crawlingly moved alongthe inner surface of a capsule body (shell) of each of microcapsules, asdistinguished from the conventional electrophoresis method. Adescription will be made on this electro-crawling method later.

However, in the display device operating with the electro-crawlingmethod, the microcapsules are arranged between a pair of electrodes, andthus if some microcapsules (shells of some microcapsules) are partiallyflattened or deformed at both or either of a display surface side and/ora back surface side of the display device, there is a problem thatdisplay contrast is reduced. Such a problem could not be found in theconventional display apparatus operating with the electrophoresismethod.

In other words, as shown in FIG. 22, an outer diameter of each of themicrocapsules 1000 is not constant, that is, the microcapsules 1000include large diameter microcapsules and small diameter microcapsules.In particular, the large diameter microcapsules 1000 are likely to bedeformed, and therefore the shapes of the large diameter microcapsules1000 become partially flattened.

Further, in the display device operating with the electro-crawlingmethod, the contact particles are moved along an inner surface of acapsule body 1100 (FIG. 22) with being in contact with the inner surfacethereof. In order to accomplish such movement of the contact particles,electric fields are needed to be generated in a tangential direction ofthe inner surface of the capsule body 1100, which are obtained byapplying an electrical voltage to between the pair of electrodes.

Therefore, the shapes of the large diameter microcapsules 1000 becomeflattened at both or either of the display surface side and/or the backsurface side of the display device. In other words, an upper innersurface and a lower inner surface of each of the large diametermicrocapsules 1000 become flat as shown in FIG. 22. If the upper andlower inner surfaces of the capsule body 1100 of the large diametermicrocapsule 1000 become parallel (flat) to an electrode 1200, itbecomes difficult for the contact particles being contact with (adheringto) the upper and lower inner surfaces of the capsule body 1100 to movealong the inner surface (side inner surface) of the capsule body 1100.

This makes it difficult for the display device to display a gray coloras shown in FIG. 22. That is, if a white color is to be displayed afterdisplaying a black color, black particles 1300 which are the contactparticles being into contact with the upper inner surface remain as theyare. This makes it difficult for the display device to display the graycolor as a display color.

On the contrary, if the black color is to be displayed after displayingthe white color, the black particles 1300 cannot be moved from the lowerinner surface to the upper inner surface so that the display colorbecomes the gray color. As a result, display contrast is reduced.

It is therefore an object of the present invention to provide a displaydevice capable of easily and reliably obtaining high display contrastand an intermediate tone and reliably maintaining individual colorsincluding the intermediate tone even at stoppage of application of anelectrical voltage. It is another object of the present invention toprovide a method of manufacturing the display device capable of easilyand reliably manufacturing the display device, and an electronicapparatus provided with the display device.

These objects are achieved by the present inventions described below.

In a first aspect of the present invention, there is provided a displaydevice. The display device comprises a microcapsule-containing layerincluding a plurality of microcapsules each having an outer diameter,wherein a variation of the outer diameters of the plurality ofmicrocapsules can be defined by an average value and a CV value.

Each of the plurality of microcapsules is comprised of: a shell havingan inner surface; contact particles electrically charged and providedwithin the shell in an contact state that the contact particles are incontact with the inner surface of the shell, and the contact particleshaving a hue; and a scattering body for scattering light, and thescattering body provided within the shell; or a colored particles havinga different hue from the hue of the contact particles, and the coloredparticles provided within the shell.

The display device further comprises a pair of electrodes that when anelectrical voltage is applied to between the pair of electrodes,electrical fields to act on the contact particles are generated. Theaverage value of the outer diameters of the plurality of microcapsulesis in the range of 20 to 60 μm, and the CV value of the outer diametersof the microcapsules is 20% or less.

In a case where the electrical voltage is applied to between the pair ofelectrodes, the contact particles are moved along the inner surface ofthe shell while maintaining the contact state with the inner surface ofthe shell.

This ensures that the contact particles (display particles) are alwaysin contact with any region on the inner surface of the shell of each ofthe microcapsule (are biased in a direction of approaching the innersurface thereof). As a result, the contact particles are reliably movedalong the inner surface thereof while maintaining the contact state.Therefore, it is possible to easily and reliably obtain an intermediatetone.

In addition, since the contact particles are biased to the inner surfaceof the shell even at stoppage of the application of the electricalvoltage to between the pair of electrodes, it is possible to reliablymaintain individual colors including the intermediate tone. In otherwords, display is highly stable and, even when the application of theelectrical voltage is stopped after a specified display content (animage) has been displayed, the display content is maintained stably(namely, it is possible to prevent deterioration of a display state).

Further, the contact particles are in contact with the inner surface ofthe shell so that they are hard to adhere to the scattering body or thecolored particles. This assists in increasing display contrast andchromatic purity. Furthermore, it is possible to reliably move thecontact particles with relatively weak electrical fields, therebyreducing power consumption of the display device.

Furthermore, since the CV value (coefficient of variation) of the outerdiameters (particle diameter) of the microcapsules is small, shapes ofthe microcapsules do not become flattened, that is, they keep aspherical shape. This makes it possible for the contact particles toreliably move along the inner surface of the shell while maintaining thecontact state when the contact particles are moved. As a result, it ispossible to reliably display individual colors including theintermediate tone, thereby obtaining high display contrast.

Furthermore, since the average value of the outer diameters of themicrocapsules falls within the above noted range, the shell is hardlycompressed. In addition to that, it is possible to provide the contactparticles and the scattering body or the colored particles of a relativelarge amount within the shell. This makes it possible for the whiteparticles to improve property of concealing the black particles when thewhite color is displayed. As a result, the white color is displayedclearly, thereby obtaining high display contrast.

Furthermore, it is possible to easily and reliably manufacture a displaydevice compared with what is called a microcup-type display device.

In the display device according to the present invention, it ispreferred that the contact particles are in contact with the innersurface of the shell due to an electrostatic force exerted therebetween.

This makes it possible to contact the contact particles to the innersurface of the shell easily and reliably.

In the display device according to the present invention, it is alsopreferred that the contact particles have a polarity, the microcapsuleshave net charges having the same polarity as the polarity of the contactparticles, and the net charges are existed within the shell, so that thecontact particles are in contact with the inner surface of the shell dueto the same polarity of the net charges.

This also makes it possible to contact the contact particles to theinner surface of the shell easily and reliably.

In the display device according to the present invention, it is alsopreferred that a force of holding the contact particles against theinner surface of the shell is greater than an electrostatic force ofacting on the contact particles due to the electrical fields generatedbetween the pair of electrodes.

With the display device, the contact particles can be moved along theinner surface of the shell with maintaining the contact state morereliably.

In the display device according to the present invention, it is alsopreferred that the scattering body or the colored particles comprise aliquid filled in the shell.

This makes it possible to obtain more excellent display performance ofthe display device.

In the display device according to the present invention, it is alsopreferred that the liquid is constituted of a liquid-phase dispersionmedium and dispersion particles dispersed in the liquid-phase dispersionmedium.

This also makes it possible to obtain more excellent display performanceof the display device.

In the display device according to the present invention, it is alsopreferred that the dispersion particles comprise particles of scatteringlight or colored particles.

This also makes it possible to obtain more excellent display performanceof the display device.

In the display device according to the present invention, it is alsopreferred that the contact particles have a polarity, and the dispersionparticles are not substantially electrically charged, or the dispersionparticles are electrically charged in an opposite polarity as thepolarity of the contact particles.

This makes it possible to prevent the dispersion particles from beingcontact with the inner surface of the shell by being biased in adirection of approaching the inner surface of the shell.

In the display device according to the present invention, it is alsopreferred that the scattering body or the colored particles is/are astructural body provided within the shell so as to be spaced apart fromthe inner surface of the shell to a predetermined distance, and thestructural body having an outer surface. The contact particles arepositioned between the inner surface of the shell and the outer surfaceof the structural body.

This also makes it possible to obtain more excellent display performanceof the display device.

In the display device according to the present invention, it is alsopreferred that the contact particles are colored particles.

This also makes it possible to obtain more excellent display performanceof the display device.

In the display device according to the present invention, it is alsopreferred that the pair of electrodes are provided opposite to eachother through the microcapsule-containing layer, and a shape of eachshell is a spherical shell shape.

This makes it possible for the contact particles to smoothly andreliably move along the inner surface of the shell having the sphericalshell shape. Therefore, it is possible to obtain individual colorsincluding the intermediate tone more easily and reliably.

In the display device according to the present invention, it is alsopreferred that the display device has a side surface, and an averageroundness R of the microcapsules represented by the following formula(I) is in the range 0.88 to 1 when viewed from the side surface of thedisplay device.

R=L₀/L₁  (I)

L₁ (μm) represents a circumference of a projected image of themicrocapsule that is a subject of measurement, and L₀ (μm) represents acircumference of a perfect circle having the same area as that of theprojected image of the microcapsule that is the subject of measurement.

This makes it possible for the contact particles to smoothly andreliably move along the inner surface of the shell. Therefore, it ispossible to obtain individual colors including the intermediate tonemore easily and reliably.

In the display device according to the present invention, it is alsopreferred that the shell comprises a first layer and a second layerarranged outside the first layer, and each of the first layer and thesecond layer has a shell-like shape.

This makes it possible to manufacture the display device easily.

In the display device according to the present invention, it is alsopreferred that the display surface has a display surface, positions ofthe contact particles included in the microcapsules are adjusted byadjusting of a magnitude of the electrical voltage to be applied tobetween the pair of electrodes and/or a time of applying the electricalvoltage to between the pair of electrodes, so that when the displaydevice is viewed from the display surface, a ratio of an area of aregion in which the contact particles provided within the shell areviewed and an area of a region in which the scattering body or thecolored particles provided within the shell is/are viewed is adjustable.

This makes it possible to obtain an intermediate tone more easily andreliably.

In a second aspect of the present invention, there is provided a methodof manufacturing a display device. The method comprises amicrocapsule-containing layer formation step for forming amicrocapsule-containing layer including a plurality of microcapsuleseach having an outer diameter and a shell having an inner portion withan inner surface.

Each of the microcapsules is produced by encapsulating a plurality ofelectrically charged contact particles having a hue and a polarity, anda scattering body for scattering light or a colored particles for havinga different hue from the hue of the contact particles. A CV value of theouter diameters of the microcapsules is 20% or less.

The method further comprises an electrode formation step for forming apair of electrodes that when an electrical voltage is applied to betweenthe pair of electrodes, electrical fields to act on the contactparticles are generated.

The microcapsule-containing layer formation step comprises a chargingstep for providing net charges, of which polarity is the same as thepolarity of the contact particles, to the inside of the shell afterforming the inner portion or the entirety of the shell, so that thecontact particles are in contact with the inner surface of the shell.

This makes it possible to manufacture the display device according tothe present invention easily and reliably.

In the method of manufacturing the display device according to thepresent invention, it is preferred that the shell comprises a firstlayer corresponding to the inner portion and a second layer arrangedoutside the first layer, and each of the first layer and the secondlayer has a shell-like shape, and the charging step is performed whenforming the second layer.

This also makes it possible to manufacture the display device accordingto the present invention more easily and reliably.

In the method of manufacturing the display device according to thepresent invention, it is also preferred that each of the microcapsuleshas an outer surface opposite to the side of the inner portion with theinner surface.

In the microcapsule-containing layer formation step, themicrocapsule-containing layer is formed using a microcapsule coatingmaterial prepared by mixing the microcapsules with a fixing materialthat makes close contact with the outer surface of each of themicrocapsules to fix the microcapsules in place, and the charging stepis performed after the microcapsule-containing layer formation step.

This also makes it possible to manufacture the display device accordingto the present invention more easily and reliably.

In a third aspect of the present invention, there is provided anelectronic apparatus provided with the above display device.

This makes it possible to provide an electronic apparatus with excellentdisplay performance.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a vertical section view (section-side view) schematicallyshowing a first embodiment of a display device according to the presentinvention.

FIG. 2 is a pattern diagram for explaining behavior of the displaydevice shown in FIG. 1.

FIG. 3 is a pattern diagram for explaining behavior of the displaydevice shown in FIG. 1.

FIG. 4 is a graph (a potential curve) showing a relationship of adistance between a surface of each of contact particles and an innersurface of a capsule body to potential of the contact particle in thedisplay device shown in FIG. 1.

FIG. 5 is a pattern diagram for explaining behavior of the displaydevice shown in FIG. 1.

FIGS. 6A to 6C are pattern diagrams for explaining behavior of thedisplay device shown in FIG. 1.

FIGS. 7A to 7D are pattern diagrams for explaining a method ofmanufacturing the display device shown in FIG. 1.

FIGS. 8E to 8G are pattern diagrams for explaining a method ofmanufacturing the display device shown in FIG. 1.

FIGS. 9A to 9E are pattern diagrams (section views) for explaining aprinciple of the display device shown in FIG. 1.

FIG. 10 is a pattern diagram (section view) showing a firstconfiguration example of a microcapsule provided in the display deviceshown in FIG. 1.

FIG. 11 is a pattern diagram (section view) showing a secondconfiguration example of a microcapsule and a near-field region thereof(binder) provided in the display device shown in FIG. 1.

FIG. 12 is a pattern diagram (section view) showing a thirdconfiguration example of a microcapsule provided in the display deviceshown in FIG. 1.

FIG. 13 is a pattern diagram (section view) showing a fourthconfiguration example of a microcapsule and a near-field region thereof(binder) provided in the display device shown in FIG. 1.

FIG. 14 is a pattern diagram (section view) showing a configurationexample of a microcapsule provided in a conventional display device.

FIG. 15 is a section view schematically showing a configuration exampleof a major part of a micro reactor 9.

FIGS. 16A and 16B are pattern diagrams for explaining another method ofmanufacturing the display device shown in FIG. 1.

FIG. 17 is a vertical section view schematically showing a fourthembodiment of a display device according to the present invention.

FIG. 18 is a perspective view showing an embodiment in which anelectronic apparatus according to the present invention is used in anelectronic paper.

FIGS. 19A and 19B are section and plan views showing an embodiment inwhich an electronic apparatus according to the present invention is usedin a display apparatus.

FIG. 20 is an electron microscope photograph of microcapsules when awhite color is displayed after a black color is displayed in a displaydevice obtained in Example 23.

FIG. 21 is an electron microscope photograph of microcapsules when awhite color is displayed after a black color is displayed in a displaydevice obtained in Comparative Example 10.

FIG. 22 is a vertical section view (section-side view) schematicallyshowing a display device operating with an electro-crawling method.

DESCRIPTION OF EXEMPLARY EMBODIMENTS

Hereinafter, a display device, a method of manufacturing a displaydevice and an electronic apparatus in accordance with the presentinvention will be described in detail with reference to preferredembodiments shown in the accompanying drawings.

First Embodiment

1. Display Device

First, a description will be made on a display device according to thepresent invention.

FIG. 1 is a vertical section view (section-side view) schematicallyshowing a first embodiment of a display device according to the presentinvention. FIGS. 2 and 3 are pattern diagrams for explaining behavior ofthe display device shown in FIG. 1.

FIG. 4 is a graph (a potential curve) showing a relationship of adistance between a surface of each of contact particles and an innersurface of a capsule body to potential of the contact particle in thedisplay device shown in FIG. 1.

FIG. 5 is a pattern diagram for explaining behavior of the displaydevice shown in FIG. 1. Further, FIGS. 6A to 6C are also patterndiagrams for explaining behavior of the display device shown in FIG. 1.FIG. 6A is a vertical section view showing the display device. FIG. 6Bis a side view showing the display device. FIG. 6C is a planner viewwhen the display device is viewed from a display surface thereof.

FIGS. 7A to 7D and FIGS. 8E to 8G are pattern diagrams for explaining amethod of manufacturing the display device shown in FIG. 1. FIGS. 9A to9E are pattern diagrams (section views) for explaining a principle ofthe display device shown in FIG. 1.

FIG. 10 is a pattern diagram (section view) showing a firstconfiguration example of a microcapsule provided in the display deviceshown in FIG. 1. FIG. 12 is a pattern diagram (section view) showing athird configuration example of a microcapsule provided in the displaydevice shown in FIG. 1. FIG. 11 is a pattern diagram (section view)showing a second configuration example of a microcapsule and anear-field region thereof (binder) provided in the display device shownin FIG. 1.

FIG. 13 is a pattern diagram (section view) showing a fourthconfiguration example of a microcapsule and a near-field region thereof(binder) provided in the display device shown in FIG. 1. FIG. 14 is apattern diagram (section view) showing a configuration example of amicrocapsule provided in a conventional display device.

Hereinafter, the upper side in each of FIGS. 1 to 3, 5, 7A to 7D, and 8Eto 8G will be referred to as “upper” and the lower side will be referredto as “lower” for the purpose of convenience in the description.Further, in each of FIGS. 2, 3, 5, 6A to 6C, 9A to 9E, and 10 to 13, aconstruction of a capsule body 401 is simplified so that theconstruction thereof is shown as a single layer construction.

Furthermore, in each of FIGS. 6A to 6C, 9A to 9E, and 10 to 13,reference numerals of a liquid-phase dispersion medium 6 and dispersionparticles 5 and diagonal lines representing sections thereof areomitted.

Furthermore, in each of FIGS. 6B and 6C, the capsule bodies 401 aresection views to show insides thereof.

As shown in FIG. 1, the display device 20 includes a display sheet (afront plane) 21, a circuit board (a back plane) 22, an adhesive agentlayer 8 for bonding the display sheet 21 and the circuit board 22together, and a sealing part 7 for air-tightly sealing a gap between thedisplay sheet 21 and the circuit board 22.

The display sheet 21 includes a base substrate 12, which has aplate-like base portion 2 and a second electrode 4 formed on a lowersurface of the base portion 2, and a microcapsule-containing layer 400arranged on a lower surface (one major surface) of the base substrate 12(the second electrode 4) and comprised of a plurality of microcapsules40 and a binder 41.

On the other hand, the circuit board 22 includes an opposite substrate11, which has a plate-like base portion 1, and a plurality of firstelectrodes 3 formed on an upper surface of the base portion 1, andcircuits (not shown) provided in the opposite substrate 11 (on the baseportion 1), the circuits including switching elements such as TFTs andthe like.

A construction of the respective parts will be now described one afteranother.

The base portions 1 and 2 are formed from a sheet-like (plate-like)member and have a function of supporting or protecting the respectivemembers arranged therebetween.

Although the base portions 1 and 2 may be either flexible or rigid, itis preferred that the base portions 1 and 2 have flexibility. Use of thebase portions 1 and 2 having flexibility makes it possible to provide aflexible display device 20, namely, a display device 20 useful inconstructing, e.g., an electronic paper.

In the case where the base portions (base material layers) 1 and 2 areflexible, examples of a constituent material of each of them includepolyolefin such as polyethylene, modified polyolefin, polyamide,thermoplastic polyimide, polyether, polyether ether ketone, variouskinds of thermoplastic elastomers such as a polyurethane-based elastomerand a chlorinated polyethylene-based elastomer, copolymers mainlyconstituted of the above materials, blends mainly constituted of theabove materials, polymer alloys mainly constituted of the abovematerials, and the like. One or more of these materials may be usedindependently or in combination.

An average thickness of each of the base portions 1 and 2 is notparticularly limited to a specific value, but may be arbitrarily setdepending on the constituent material and use thereof.

In the case where the base portions 1 and 2 are flexible, the averagethickness of each of the base portions 1 and 2 is preferably in therange of about 20 to 500 μm, and more preferably in the range of about25 to 250 μm. This makes it possible to reduce the size (especially, thethickness) of the display device 20, while harmonizing flexibility andstrength of the display device 20.

The first electrodes 3 and the second electrode 4 (a pair of electrodes)are of a layered shape (a film shape) and are respectively arranged onboth sides of the microcapsule-containing layer 400. In other words, thefirst electrodes 3 and the second electrode 4 are provided in a mutuallyfacing relationship through the microcapsule-containing layer 400.

In this embodiment, the first electrodes 3 are formed on the uppersurface of the base portion 1 and the second electrode 4 is formed onthe lower surface of the base portion 2.

If an electrical voltage is applied to between the first electrodes 3and the second electrode 4, electrical fields are generated across themso that the electrical fields act on contact particles (displayparticles) 50, which will be described below, present in themicrocapsule-containing layer 400.

In this regard, it is to be noted that in the case where dispersionparticles (display particles) 5 described later are electricallycharged, the electrical fields also act on the dispersion particles 5.

In this embodiment, the second electrode 4 serves as a common electrodeand the first electrodes 3 function as individual electrodes divided ina form of a matrix (pixel electrodes connected to the switchingelements). A portion where the second electrode 4 is overlapped with oneof the first electrodes 3 constitutes a unit pixel.

Just like the first electrodes 3, the second electrode 4 may also bedivided into a plurality of electrodes. Furthermore, the firstelectrodes 3 may be divided into a plurality of stripe-shaped electrodesand, similarly, the second electrode 4 may also be divided into aplurality of stripe-shaped electrodes. In this case, the firstelectrodes 3 and the second electrode 4 may be arranged to intersectwith each other.

A constituent material of each of the first electrodes 3 and the secondelectrode 4 is not particularly limited to a specific type as long as itis substantially conductive. Various kinds of conductive materials maybe used as the constituent material of each of the first electrodes 3and the second electrode 4.

Examples of such a conductive material include: a metallic material suchas copper, aluminum or alloy containing these metals; a carbon-basedmaterial such as carbon black; an electronically conductive polymermaterial such as polyacetylene, polyfluorene or derivatives thereof; anion-conductive polymer material produced by dispersing an ionicsubstance such as NaCl or Cu(CF₃SO₃)₂ in a matrix resin such aspolyvinyl alcohol or polycarbonate; and a conductive oxide material suchas indium oxide (IO); and the like. One or more of these materials maybe used independently or in combination.

An average thickness of each of the first electrodes 3 and the secondelectrode 4 is not particularly limited to a specific value, but may bearbitrarily set depending on the constituent material and use thereof.The average thickness of each of the first electrodes 3 and the secondelectrode 4 is preferably in the range of about 0.05 to 10 μm, and morepreferably in the range of about 0.05 to 5 μm.

Among the base portions 1 and 2 and the first electrodes 3 and thesecond electrode 4, the ones arranged on a display surface side (thebase portion 2 and the second electrode 4 in this embodiment) areoptically transparent, i.e., substantially transparent (clear andcolorless, clear and colorful, or translucent).

This makes it possible to easily recognize, through visual observation,statuses of the contact particles 50 and the dispersion particles 5described below, i.e., information (images) displayed by the displaydevice 20.

In the display sheet 21, the microcapsule-containing layer 400 isprovided in contact with a lower surface of the second electrode 4. Themicrocapsule-containing layer 400 includes a plurality of microcapsulesand a binder (a fixing material) 41 for fixing (or holding) themicrocapsules 40 in place, each of the microcapsules 40 having a capsulebody (shell) 401, and a dispersion liquid 10 described below and thecontact particles 50 encapsulated into the capsule body 401.

Hereinafter, the microcapsule-containing layer 400 will be described,but the microcapsules 40 will be described below in detail.

The binder 41 makes close contact with an outer surface of each of themicrocapsules 40 and covers each of the microcapsules 40. Gaps(interstices) formed among the microcapsules 40 are filled with thebinder 41.

The binder 41 is provided between the opposite substrate 11 and the basesubstrate 12 for the purpose of, e.g., bonding the opposite substrate 11and the base substrate 12 together, fixing the microcapsules 40 betweenthe opposite substrate 11 and the base substrate 12, assuring insulationbetween the first electrodes 3 and the second electrode 4, andgenerating strong electrical fields by filling the gaps among themicrocapsules 40 therewith. This makes it possible to further improvedurability, reliability and display performance of the display device20.

Preferably used as the binder 41 is a resin material that exhibits highaffinity with (improved adhesion to) the respective electrodes 3 and 4and the capsule bodies 401 (of the microcapsules 40) and has increasedinsulation performance and relatively high permittivity which does notallow a current to flow at all or allows a current to slightly flow.

Examples of such a resin material used as the binder 41 include: athermoplastic resin such as polyethylene, polypropylene, an ABS resin, amethacrylate resin (e.g., a methyl methacrylate resin), a vinyl chlorideresin or a cellulose-based resin; a silicone-based resin; anurethane-based resin; and the like. One or more of these materials maybe used independently or in combination.

In this embodiment, the display sheet 21 and the circuit board 22 arebonded together by means of the adhesive agent layer 8. This makes itpossible to fix the display sheet 21 and the circuit board 22 in areliable manner. It is preferred that the adhesive agent layer 8 ismainly constituted of polyurethane.

The polyurethane contains an isocyanate component and a polyolcomponent. The isocyanate component may be, e.g., at least one kind oftetramethylxylene diisocyanate (TMXDI), hexamethylene diisocyanate(HMDI) and derivatives thereof. The polyol component may be, e.g., atleast one kind of polypropylene glycol (PPG), polytetramethylene glycol(PTMG) and derivatives thereof.

A constituent material of the adhesive agent layer 8 is not limited tothe polyurethane. In addition to the polyurethane, examples of theconstituent material of the adhesive agent layer 8 further include aresin material such as polyethylene, chlorinated polyethylene, ABSresin, vinyl acrylate copolymer, a fluorine-based resin or asilicone-based resin, and the like. One or more of these materials maybe used independently or in combination.

The sealing part 7 is provided between the base portions 1 and 2, andalong peripheral edges of the first electrodes 3, the second electrode4, the microcapsule-containing layer 400, and the adhesive agent layer8. The first electrodes 3, the second electrode 4, themicrocapsule-containing layer 400, and the adhesive agent layer 8 areair-tightly sealed by means of the sealing part 7.

This makes it possible to prevent moisture from infiltrating into thedisplay device 20, thereby reliably avoiding degradation in displayperformance of the display device 20.

Various kinds of resin materials can be used as a constituent materialof the sealing part 7. Examples of such resin materials include: athermoplastic resin such as an acryl-based resin, an urethane-basedresin or an olefin-based resin; a thermosetting resin such as anepoxy-based resin, a melamine-based resin or a phenol-based resin; andthe like. One or more of these resin materials may be used independentlyor in combination.

In this regard, it is to be noted that the sealing part 7 may be eitherprovided or removed depending on the circumstances.

The contact particles (electrically charged particles) 50 are in contactwith (adhere to) the inner surface of the capsule body 401 of each ofthe microcapsules 40 by being biased in a direction of approaching theinner surface thereof. That is, the contact particles 50 are held in astate of being capable of moving along the inner surface of the capsulebody 401.

In other words, the contact particles 50 are electrically charged with aspecified polarity. Further, net charges exist inside the capsule body401 (not include the capsule body 401 in itself) as will be set forthlater. The net charges, which are a total value (summation) of totalcharges including charges of the contact particles 50, are not zero.

A polarity of the net charges is the same (same polarity) as that of thecharges of the contact particles 50. Therefore, the contact particles 50are in contact with (are biased) the inner surface of the capsule body401 due to repulsive force (repelling force) occurring by electrostaticforce between the charges of contact particles 50 and the charges of thenet charges of which polarity is the same polarity as that of thecontact particles 50.

Thus, the contact particles 50 adhere to the inner surface of thecapsule body 401 in a movable state. In this regard, it is to be notedthat the contact particles 50 look like adsorbing to the inner surfaceof the capsule body 401 in appearance.

Hereinafter, each force acting on the contact particles 50 inside thecapsule body 401 is a force based on the inner surface of the capsulebody 401 as long as each force is not particularly referred to aspecific force. The force acting in the direction of approaching theinner surface of the capsule body 401 (a direction of proceeding tooutside of the capsule body 401) is referred to as “attractive force”.The force acting in a direction apart from the inner surface of thecapsule body 401 (a direction of proceeding to a center portion of thecapsule body 401) is referred to as “repulsive force”.

The contact particles 50 may include one or more kinds of particles. Itis preferred that colored particles are used as the contact particles50. In this embodiment, black particles (colored particles) fordisplaying a black color are used as the contact particles 50.

In this embodiment, a liquid, namely a dispersion liquid 10 isencapsulated (or filled) inside the capsule body 401 as a scatteringbody for scattering light or colored particles having a different hue(color phase) from that of the contact particles 50.

The dispersion liquid 10 is constituted of a liquid-phase dispersionmedium 6 and dispersion particles 5 dispersed (suspended) in theliquid-phase dispersion medium 6. The dispersion particles 5 may includeone or more kinds of particles. It is preferred that particles forscattering light or colored particles having a different hue from thatof the contact particles 50 are used as the dispersion particles 5.

In this embodiment, the particles for scattering the light (namely,white particles to display a white color) are used as the dispersionparticles 5. In other words, in this embodiment, the dispersionparticles 5 to scatter the light are dispersed in the liquid-phasedispersion medium 6, which are used as the dispersion liquid 10(scattering body or colored particles). In this regard, it is to benoted that the white color is displayed by scattering the light.

A liquid for scattering light or a liquid containing no particles andhaving a different hue from that of the contact particles 50 may be usedinstead of the dispersion liquid 10. Further, gas for scattering thelight or gas having the different hue from that of the contact particles50 may be used instead of the dispersion liquid 10.

The dispersion particles 5 may be electrically charged or notelectrically charged. In a case where the dispersion particles 5 areelectrically charged, the dispersion particles 5 are needed to beelectrically charged to the opposite polarity as that of the contactparticles 50, namely the same polarity as that of the capsule body 401.

This makes it possible to prevent the contact particles 50 from being incontact with (adhering to) the inner surface of the capsule body 401 bybeing biased in the direction of approaching the inner surface thereof.

On the other hand, in a case where the dispersion particles 5 are notsubstantially electrically charged, it is possible to prevent thedispersion particles 5 and the contact particles 50 from being adsorbedto each other.

Further, in a case where the dispersion particles 5 are electricallycharged to the opposite polarity to that of the contact particles 50,the polarity of the charges of contact particles 50 becomes the oppositeas that of the net charges inside the capsule body 401. For this reason,a phenomenon that the dispersion particles 5 are pushed (adsorbed) tothe inner surface of the capsule body 40 does not occur. Therefore, adispersion state of the dispersion particles 5 is maintained in theliquid-phase dispersion medium 6.

In this regard, in this embodiment, it is to be noted that thedispersion particles 5 are not substantially electrically charged, andare uniformly dispersed in the liquid-phase dispersion medium 6.

A task of dispersing the dispersion particles 5 and the contactparticles 50 in the liquid-phase dispersion medium 6 in producing themicrocapsules 40 can be performed by using one or more of, e.g., a paintshaker method, a ball mill method, a media mill method, an ultrasonicdispersion method and a stirrer dispersion method.

A liquid that exhibits low solubility to the capsule body 401 and hasrelatively high insulation performance is preferably used as theliquid-phase dispersion medium 6.

Examples of the liquid-phase dispersion medium 6 include: waters such asdistilled water and deionized water; alcohols such as methanol;cellosolves such as methyl cellosolve; esters such as methyl acetate;ketones such as acetone; aliphatic hydrocarbons (liquid paraffins) suchas pentane; alicyclic hydrocarbons such as cyclohexane; aromatichydrocarbons such as benzene; halogenated hydrocarbons such as methylenechloride; aromatic heterocycles such as pyridine; nitriles such asacetonitrile; amides such as N,N-dimethylformamide; carboxylic salts;oils such as silicone oil; and the like. One or more of them may be usedindependently or in combination.

Among them, it is preferable to use hydrocarbons each having a boilingpoint of 80° C. or higher or the silicone oil as the liquid-phasedispersion medium 6.

Further, if necessary, various kinds of additives may be added to theliquid-phase dispersion medium 6 (dispersion liquid 10). Examples ofsuch additives include: a charge-controlling agent formed of particlesof an electrolyte, a (anionic or cationic) surfactant such asalkenylsuccinate, a metal soap, a resin material, a rubber material, anoil, a varnish or a compound; a dispersion agent such as a silane-basedcoupling agent; a lubricating agent; a stabilizing agent; and the like.

Further, in a case where the liquid-phase dispersion medium 6 iscolored, if necessary, a dye may be dissolved therein. Examples of thedye include an anthraquinone-based dye, an azo-based dye, anindigoid-based dye, and the like.

The contact particles 50 are charged particles capable of, under theaction of the electrical fields, moving along the inner surface of thecapsule body 401 in the liquid-phase dispersion medium 6. In otherwords, the contact particles 50 are moved along the inner surface of thecapsule body 401 while maintaining the contact state as will bedescribed later.

On the other hand, the dispersion particles 5 may be the chargedparticles capable of, under the action of the electrical fields,electrophoresing in the liquid-phase dispersion medium 6 as describedabove. Further, the dispersion particles 5 may not be the chargedparticles.

The contact particles 50 may be any kind of particles insofar as theyhave electrical charges. Further, the dispersion particles 5 may be anykind of particles insofar as they are particles for scattering the lightor colored particles having the different hue from that of the contactparticles 50, regardless of the charged particles (electrical charges).

Although not particularly limited, at least one of pigment particles,resin particles and composite particles thereof may be preferably usedas the contact particles 50 and the dispersion particles 5. Use of theseparticles provides an advantage in that they are easy to produce, whileassuring easier control of electrical charges.

Examples of a pigment of which the pigment particles are made include: ablack pigment such as aniline black, carbon black or titanium black; awhite pigment such as titanium oxide or antimony oxide; an azo-basedpigment such as monoazo; a yellow pigment such as isoindolinone orchrome yellow; a red pigment such as quinacridone red or chromevermilion; a blue pigment such as phthalocyanine blue or indanthreneblue; a green pigment such as phthalocyanine green; and the like. One ormore of these pigments may be used independently or in combination.

Examples of a resin material of which the resin particles are madeinclude an acryl-based resin, an urethane-based resin, an urea-basedresin, an epoxy-based resin, polystyrene, polyester and the like. One ormore of these resin materials may be used independently or incombination.

Examples of the composite particles include: particles produced bycoating surfaces of the pigment particles with the resin material orother pigment; particles produced by coating surfaces of the resinparticles with the pigment; and particles made of a mixture obtained bymixing the pigment and the resin material in a suitable compositionratio.

Examples of the particles produced by coating the surfaces of thepigment particles with the other pigment include particles obtained bycoating surfaces of titanium oxide particles with silicon oxide oraluminum oxide. These particles are preferably used as the dispersionparticles 5 for displaying a white color.

Carbon black particles, titanium black particles or particles producedby coating surfaces of these particles with other material arepreferably used as the contact particles 50 for displaying a blackcolor.

Further, shapes of the contact particles 50 and the dispersion particles5 are not particularly limited to a specific type, but may preferably bea spherical shape.

It is preferred that contact particles 50 and the dispersion particles 5each having a relatively small size are used. More specifically, anaverage particle size of each of the contact particles 50 and thedispersion particles 5 is preferably in the range of about 10 nm to 3μm, more preferably in the range of about 20 nm to 2 μm, and even morepreferably in the range of about 20 nm to 800 nm.

If the average particle size of each of the contact particles 50 and thedispersion particles 5 falls within the above-noted range, it ispossible to prevent the contact particles 50 and the dispersionparticles 5 from clumping together in the liquid-phase dispersion medium6. Further, it is possible to reliably prevent the dispersion particles5 from sinking in the liquid-phase dispersion medium 6.

Namely, the contact particles 50 and the dispersion particles 5 can bestably dispersed therein. As a result, it becomes possible to reliablyprevent degradation in display quality of the display device 20.

In the case where two different particles of different colors are usedas in this embodiment, there is no problem even that they have differentaverage particle sizes. In the display device 20 according to thepresent invention, it is possible to improve display contrast of thedisplay device 20.

As shown in FIG. 1, each of the microcapsules 40 has a sizecorresponding to a full thickness of the microcapsule-containing layer400, and the microcapsules 40 are arranged lengthwise and crosswisebetween the opposite substrate 11 and the base substrate 12 so as toform a single layer (in which the microcapsules 40 are arranged side byside with no overlap in the thickness direction of themicrocapsule-containing layer 400).

While one microcapsule 40 is aligned with one first electrode 3 in theillustrated construction, the present invention is not limited thereto.For example, two microcapsules 40 or more than two microcapsules 40 maybe aligned with one first electrode 3.

In the illustrated construction, the microcapsules 40 are kept in agenerally spherical shape without being compressed (pressed) in anup-and-down direction, even if they are sandwichedly held by the secondelectrode 4 and the adhesive agent layer 8 in between the oppositesubstrate 11 and the base substrate 12. The capsule body (the shell) 401serving as a wall structure for defining a space filled with thedispersion liquid 10 (a space within which the scattering body or thecolored particles is/are provided) is formed into a spherical shellshape.

In other words, the inner surface of the capsule body 401 is formed of acurved concave surface extending (continuously extending) between thefirst electrodes 3 and the second electrode 4. This means that no planar(flat) surface extending parallel to the first electrodes 3 and thesecond electrode 4 exists in the inner surface of the capsule body 401(upper and lower inner surfaces). This makes it possible for the contactparticles 50 to smoothly and reliably move along the inner surface (thecurved concave surface) of the capsule body 401.

In this regard, it is to be noted that the microcapsules 40 are notlimited to the spherical shape, but may be formed into, e.g., agenerally elliptical shape or other shapes. In other words, the capsulebody 401 is not limited to the spherical shape, but may be formed into,e.g., an elliptical shell shape or other shapes.

Further, the capsule body 401 and a near-field region thereof (that is,the binder 41) may be electrically charged or not be electricallycharged. In this regard, it is to be noted that this will be describedlater.

In the display device 20, the net charges exist inside the capsule body401 (not include the capsule body 401 in itself). The net charges, whichare a total value (summation) of total charges including electricalcharges of the contact particles 50, are not zero. The polarity of thenet charges is the same (same polarity) as those of the electricalcharges of the contact particles 50.

Therefore, the contact particles 50 are in contact with the innersurface of the capsule body 401 by attractive force acting between thecontact particles 50 and the capsule body 401. The attractive force is asum (total force) of the following three forces.

The first force is electrostatic force (attractive force) occurring dueto the net charges (which include the electrical charges of the contactparticles 50) existing inside the capsule body 401 (not include thecapsule body 401 in itself).

The second force is van der Waals' force (attractive force) occurringbetween the contact particles 50 and the capsule body 401. The thirdforce is repulsive force occurring due to osmotic pressure (which isgenerated by a steric stabilization treatment using a graft polymer).

Referring to FIG. 2, the contact particles 50 are in contact with(adhere to) the inner surface of the capsule body 401 and keptstationarily in a specified position when no electrical voltage isapplied to between the first electrodes 3 and the second electrode 4.Further, the dispersion particles 5 are dispersed in the liquid-phasedispersion medium 6.

All the contact particles 50 may be in contact with the inner surface ofthe capsule body 401, but not limited thereto, a part thereof may not bein contact with the inner surface of the capsule body 401. For example,in a case where the contact particles 50 are arranged on the innersurface of the capsule body 401 in a state of two layers, the two layersof the contact particles 50 are arranged as follows.

One layer of the contact particles 50 is in contact with the innersurface of the capsule body 401. The other layer of the contactparticles 50 is in contact with the one layer. This is also the same asa case during moving of the contact particles 50 described later.

If an electrical voltage is applied to between the first electrodes 3and the second electrode 4 to generate electrical fields therebetween,the contact particles 50 are moved toward one of the electrodes 3 and 4along the inner surface of the capsule body 401 under the action of theelectrical fields while maintaining the contact state. Further, thedispersion particles 5 are maintained in a state of being dispersed inthe liquid-phase dispersion medium 6.

Then, if the application of the electrical voltage is stopped, thecontact particles 50 cease to move along the inner surface of thecapsule body 401 and are stopped in a specified position whilemaintaining the contact state. Further, the dispersion particles 5 aremaintained in the state of being dispersed in the liquid-phasedispersion medium 6.

More specifically, if the contact particles 50 are negatively chargedand the net charges inside the capsule body 401 are negatively charged,and if an electrical voltage is applied to between the first electrodes3 and the second electrode 4 so that the first electrodes 3 can be in apositive electrical potential with respect to the second electrode 4,the contact particles 50 are moved along the inner surface of thecapsule body 401 toward the first electrodes 3 (toward the opposite sidefrom the display surface of the display device 20) while maintaining thecontact state.

In contrast, if an electrical voltage is applied to between the firstelectrodes 3 and the second electrode 4 so that the first electrodes 3can be in a negative electrical potential with respect to the secondelectrode 4, the contact particles 50 are moved along the inner surfaceof the capsule body 401 toward the second electrode 4 (toward thedisplay surface of the display device 20) while maintaining the contactstate.

In this case, the position of the contact particles 50 can be adjustedby applying a pulsed voltage (a pulse voltage) to between the firstelectrodes 3 and the second electrode 4, namely by regulating one orboth of magnitude (a voltage value) of the electrical voltage applied tobetween the first electrodes 3 and the second electrode 4 and a time (anapplication time) of applying the electrical voltage to between thefirst electrodes 3 and the second electrode 4.

When the display device 20 is viewed from the display surface side (theupper side in FIG. 2), namely as shown in FIG. 6C, a ratio (S2/S1) of anarea (S2) of a region in which the contact particles 50 are viewed,namely a black region in FIG. 6C, to a total area (S1) of region inwhich the dispersion particles 5 and the liquid-phase dispersion medium6 within the capsule body 401 is viewed, namely a white region in FIG.6C, can be adjusted (FIG. 6).

This makes it possible to change an amount (brightness) of lightreflected at the microcapsules 40. In this regard, it is to be notedthat each of the total area (S1) and the area (S2) is an area obtainedby projecting to a flat surface with respect to the base portion 2 (basesubstrate 12).

This makes it possible, in providing the white and black display in thisembodiment, to display an arbitrary intermediate tone (an intermediatecolor) between the white color and the black color, i.e., a gray colorof arbitrary gradation (brightness). In other words, it is possible tocontinuously change the displayed color between the white color and theblack color.

For example, when the contact particles 50 are positioned near the firstelectrodes 3 as shown on the left side in FIG. 2, namely when thecontact particles 50 are positioned in a lower hemisphere of the capsulebody 401 (a hemisphere near the first electrodes 3), namely the contactparticles are invisible as viewed from the display surface side of thedisplay device 20, the ratio (S2/S1) becomes 0, and therefore thedisplayed color becomes the white color.

In other words, almost all (most) of light incident on the microcapsules40 is scattered by the dispersion particles 5. Therefore, the displaydevice 20 is seen white when viewed from the display surface sidethereof.

When the contact particles 50 are positioned near the second electrode4, namely when the contact particles 50 are positioned in the upperhemisphere of the capsule body 401 (the hemisphere near the secondelectrode 4), namely only the contact particles are visible as viewedfrom the display surface side of the display device 20, the ratio(S2/S1) becomes 1, and therefore the displayed color becomes the blackcolor.

In other words, almost all (most) of light incident on the microcapsules40 is adsorbed by the contact particles 50. Therefore, the displaydevice 20 is seen black (the same color as the contact particles 50)when viewed from the display surface side thereof.

When the contact particles 50 are medially positioned between the firstelectrodes 3 and the second electrode 4, namely when the contactparticles 50 are distributed like a belt over upper and lowerhemispheres of the capsule body 401, namely the contact particles 5 areviewed in a form of a ring as viewed from the display surface side ofthe display device 20 (FIG. 6C), the ratio (S2/S1) becomes apredetermined value which is larger than 0 and smaller than 1, andtherefore the displayed color becomes a gray color of a predeterminedgradation.

In other words, one part of the light incident on the microcapsules 40is scattered by the dispersion particles 5, and other parts of the lightincident on the microcapsules 40 are adsorbed by the contact particles50. Therefore, the displayed color becomes the gray color of thepredetermined gradation when viewed from the display surface sidethereof.

Although there is no particular limitation in controlling the displaydevice 20, the display device 20 may be controlled in the followingmanner. For example, a state that the contact particles 50 arepositioned near the first electrodes 3, i.e. a state that the whitecolor is displayed, or a state that the contact particles 50 arepositioned near the second electrode 4, i.e., a state that the blackcolor is displayed, is set as an initial state (a reference state).

In order to display the specified intermediate tone, it is preferredthat the display device 20 is first restored to the initial state, andthen the pulse voltage is applied to between the first electrodes 3 andthe second electrode 4.

The reason for this is that it is possible to reliably restore thedisplay device 20 to the initial state by, e.g., applying an electricalvoltage to between the first electrodes 3 and the second electrode 4 fora sufficient time (namely, there is no need to finely adjust magnitudeand an application time of the electrical voltage which is applied tobetween the first electrodes 3 and the second electrode 4 to restore thedisplay device 20 to the initial state), and that it is possible toreliably display the desired intermediate tone by applying the pulsevoltage in the initial state.

As another control method, it may also be preferred that the displaydevice 20 is constructed to apply a pulse voltage required in changing acurrent display state that the intermediate tone is displayed into adisplay state that the desired intermediate tone is to be displayed.

The reason for this is that the display device 20 is capable of reliablydisplaying the intermediate tone, and that the desired intermediate tonecan be reliably displayed even if the current display state is notrestored to the initial state but successively changed into a state thatthe desired intermediate tone is to be displayed.

In this regard, it is to be noted that the electrical voltage applied tobetween the first electrodes 3 and the second electrode 4 is not limitedto a single pulse voltage, but may be multiple pulse voltages with samepolarities, or multiple pulse voltages with alternately changingpolarities (alternating voltages), or the like.

In a case where the dispersion particles 5 are electrically charged inthe opposite polarity as that of the contact particles 50, if theelectrical voltage is applied to between the first electrodes 3 and thesecond electrode 4, the dispersion particles 5 are electrophoresedtoward the opposite electrode to an electrode toward which the contactparticles 50 are electrophoresed.

However, if the application of the electrical voltage is stopped betweenthe first electrodes 3 and the second electrode 4, the dispersionparticles 5 are re-dispersed in the liquid-phase dispersion medium 6.This case exhibits the same function as that of a case where thedispersion particles 5 are not electrically charged.

As shown in FIG. 3, the display device 20 is constructed to ensure thatthe attractive force (f₂ in FIG. 3) due to the interaction between thecontact particles 50 and the capsule body 401 is greater than theelectrostatic force (f₁ in FIG. 3) acting on the contact particles 50due to the electrical fields generated between the first electrodes 3and the second electrode 4.

The attractive force (f₂) due to the interaction between the contactparticles 50 and the capsule body 40 is a sum (the resultant force) ofattractive forces occurring due to interactions among others contactparticles 50, dispersion liquid 10, and the capsule body 401, when thepredetermined contact particles 50 are focused. That is, the attractiveforces are the sum of the following three forces.

The first force is electrostatic force (attractive force) occurring dueto the net charges (which include the electrical charges of the contactparticles 50) existing inside the capsule body 401 (not include thecapsule body 401 in itself).

The second force is van der Waals' force (attractive force) occurringbetween the contact particles 50 and the capsule body 401. The thirdforce is repulsive force occurring due to osmotic pressure (which isgenerated by a steric stabilization treatment using a graft polymer).

The task of making the attractive force (f₂) greater than theelectrostatic force (f₁) can be accomplished by suitably setting, e.g.,a charge amount of the respective parts, charge density of therespective parts, namely, the net charge amount inside the capsule body401, or magnitude of the electrical voltage applied to between the firstelectrodes 3 and the second electrode 4.

Therefore, when the electrical voltage is applied to between the firstelectrodes 3 and the second electrode 4 and when the electrical fieldsgenerated therebetween act on the contact particles 50, the resultantforce (f₃ in FIG. 3) of the electrostatic force (f₁) and the attractiveforce (f₂) acts in a direction as shown in FIG. 3.

This makes it possible to prevent the contact particles 50 from movingaway from the capsule body 401, which ensures that the contact particles50 are reliably moved along the inner surface of the capsule body 401while maintaining the contact state.

The phenomenon that the contact particles 50 are moved along the innersurface of the capsule body 401 while maintaining the contact state isquite complex in view of a microscopic standpoint, as will be describedbelow.

More specifically, a relationship (the attractive force, and repulsiveforce, etc.) between the contact particles 50 and the capsule body 401is significantly complex. The interactions among predetermined contactparticles 50, other contact particles 50, the dispersion liquid 10, andthe capsule body 401 can be explained using a potential curveillustrated in FIG. 4.

As illustrated in FIG. 4, in the potential curve, a valley of potentialis created when summing up the electrostatic force occurring due to thenet charges existing inside the capsule body 401, the van der Waals'force occurring between the contact particles 50 and the capsule body401, and the repulsive force occurring due to the osmotic pressure.

When a distance between a surface of each of the contact particles 50and the inner surface of the capsule body 401 is Z₀ in FIG. 4, thecontact particles 50 are held to the inner surface of the capsule body401 in a position in which the surface of each of the contact particles50 are spaced apart from the inner surface of the capsule body 401 bythe distance Z₀. The distance Z₀ is on the order of nanometers. In thiscase, if the surfaces of the contact particles 50 have polymer chains,the polymer chains of the contact particles 50 and the capsule body 401are in contact with each other.

If electrical fields are generated between the first electrodes 3 andthe second electrode 4 in this state, the contact particles 50 areeasily moved away from the inner surface of the capsule body 401. Thisis because a slope of the potential curve is zero in the position spacedapart by the distance Z₀.

As the contact particles 50 approach a position spaced apart by adistance Z₁, however, the slope of the potential curve becomes greater,thereby allowing an increased attractive force to act on the contactparticles 50. Thus, the contact particles 50 are no longer able to moveaway from the inner surface of the capsule body 401 and, instead, aremoved toward the inner surface of the capsule body 401.

As a result, if the electrical fields are generated between the firstelectrodes 3 and the second electrode 4, the contact particles 50 movealong the inner surface of the capsule body 401. At this time, each ofthe contact particles 50 moves along the inner surface of the capsulebody 401 while slightly changing the distance between the surfacethereof and the inner surface of the capsule body 401 (while slightlybouncing up and down on the inner surface of the capsule body 401) asillustrated in FIG. 5.

In this embodiment, the capsule body (the shell) 401, into which thedispersion liquid 10 and the contact particles 50 are encapsulated,includes a first capsule layer (a first layer) 402 with the innersurface and a second capsule layer (a second layer) 403 arranged outsidethe first capsule layer 402, as shown in FIG. 1.

The first capsule layer 402 and the second capsule layer 403 arerespectively formed into a spherical shell shape (a shell-like shape).An outer surface of the first capsule layer 402 is covered with thesecond capsule layer 403. This makes it possible to synergisticallyimpart characteristics of the first capsule layer 402 and the secondcapsule layer 403 to the capsule body 401.

In the capsule body 401, one or both of the first capsule layer 402 andthe second capsule layer 403 may be electrically charged, or may not beelectrically charged.

Examples of a constituent material of each of the first capsule layer402 and the second capsule layer 403 include a material containing gumsuch as gum arabic or the like, a composite material of gum arabic andgelatin, various kinds of resin materials such as an urethane-basedresin, an acryl-based resin, an epoxy-based resin, a melamine-basedresin, an urea-based resin, polyamide and polyether, and the like. Oneor more of them can be used independently or in combination.

A cross-linking agent may be added to the resin of which each of thefirst capsule layer 402 and the second capsule layer 403 is made, sothat the first capsule layer 402 and the second capsule layer 403 canhave a cross-linked (three-dimensionally cross-linked) structure. Thismakes it possible to increase strength of each of the first capsulelayer 402 and the second capsule layer 403. As a consequence, it ispossible to surely prevent the microcapsules 40 from being collapsed.

In this regard, charging or non-charging, a charge amount, chargedensity and a polarity of each of the first capsule layer 402 and thesecond capsule layer 403 are also affected by the liquid-phasedispersion medium 6. Therefore, the constituent material (thecombination of components of the constituent material), a mixing ratioof the components and various forming conditions of each of the firstcapsule layer 402 and the second capsule layer 403 are suitably setdepending on the liquid-phase dispersion medium 6 to be used.

By doing so, the net charges are existed within the capsule body 401,while adjusting the charge amount and the polarity thereof. In thiscase, additives such as a charging agent and the like may be added tothe constituent material of each of the first capsule layer 402 and thesecond capsule layer 403.

Further, it is preferred that the first capsule layer 402 and the secondcapsule layer 403 are chemically bonded together in their interfacialsurfaces. This makes it possible to reliably prevent any separation ofthe first capsule layer 402 and the second capsule layer 403 even whenpressure is applied to between the circuit board 22 and the displaysheet 21.

As a result, it is possible to reliably prevent the microcapsules 40from being collapsed due to the pressure applied at the time of bondingthe microcapsule-containing layer 400 and the circuit board 22 togetheror due to an impact and a pressing force applied when the microcapsules40 are used and stored as the display device 20.

A thickness of the capsule body 401 (a total sum of a thickness of thefirst capsule layer 402 and a thickness of the second capsule layer 403in this embodiment) is not particularly limited to a specific value, butmay be preferably in the range of 0.1 to 5 μm, more preferably in therange of 0.1 to 4 μm, and even more preferably in the range of 0.1 to 3μm in a wet state.

If the thickness of the capsule body 401 is too small, there is a fearthat great enough capsule strength of the capsule body 401 may not beobtained depending on combination of the constituent materials of thefirst capsule layer 402 and the second capsule layer 403.

In contrast, if the thickness of the capsule body 401 is too great,there is a fear that the transparency may be reduced depending on thecombination of the constituent materials of the first capsule layer 402and the second capsule layer 403, which may lead to reduction in thedisplay contrast of the display device 20.

Although the capsule body 401 has two layers consisting of the firstcapsule layer 402 and the second capsule layer 403 in this embodiment,the capsule body 401 is not limited to this two layer construction, butmay have a single layer construction or a multiple layer constructionwith three or more layers.

As for an outer particle size (outer diameter) of the capsule body 401,a volume-average particle size (average value) thereof is preferably inthe range of 20 to 60 μm, more preferably in the range of 20 to 50 μm,and even more preferably in the range of 30 to 45 μm. If the outerparticle size of the capsule body 401 falls within such a range, it ispossible to form the microcapsule-containing layer 400 with increaseddimensional accuracy. In this regard, it is to be noted that the outerparticle size of the capsule body 401 is the same as an outer particlesize of microcapsule 40.

In this case, if the outer particle size of the capsule body 401 issmaller than the lower limit value noted above, the amount of thecontact particles 50 or the dispersion particles 5 has to be reduced.For example, the white particles reduce property of concealing the blackparticles when the white display. As a result, the white color is notdisplayed clearly (e.g. a gray color), and therefore there is a fearthat the display contrast of the display device 20 is reduced.

In contrast, if the outer particle size of the capsule body 401 isgreater than the upper limit value noted above, the gaps among themicrocapsules 40 and between the base substrate 12 and the oppositesubstrate 11 (circuit substrate 22) grows smaller. That is, a number ofthe microcapsules included in the microcapsule-containing layer isreduced. Therefore, the capsule body 401 is crashed easily. As a result,there is a fear that the display contrast of the display device 20 isreduced.

It is preferred that the microcapsules 40 are formed to have a generallyuniform or equal size (particle size).

More specifically, a coefficient of variation (a CV value) of the outerdiameters (particle diameter) of the microcapsules 40 (capsule body 401)is preferably 20% or less, more preferably 15% or less, and even morepreferably 10% or less.

A lower limit value of the CV value of the outer diameters (particlediameter) of the microcapsules 40 is preferably 3%. In this regard, itis to be noted that the CV value is a value in which a standarddeviation (σ) of the outer diameters of the microcapsules 40 is dividedby an average value thereof. If the CV value is too small, the width ofa particle size distribution (particle diameter distribution) of themicrocapsules 40 is small so that the outer diameters of themicrocapsules 40 are uniform.

If the CV value of the outer diameters of the microcapsules 40 exceedsthe upper limit value noted above, the shapes of the relative largemicrocapsules 40 become flattened, so that it becomes difficult for thecontact particles 50 to move along the inner surface of the capsule body401 as described above.

As described above, the display color of the display device 20 becomesthe gray color as shown in FIG. 22. That is, if the white color is to bedisplayed after displaying the black color, the black particles 1300which are the contact particles 50 being into contact with (attachingto) the upper inner surface (flat surface) remain to the upper innersurface.

In other words, a phenomenon, that the display color of the middleregion of each of the microcapsules 40 becomes the black color as viewedthe display surface side of the display device 20, occurs. This makes itpossible to display a gray color.

On the contrary, although not shown in draws, if the black color is tobe displayed after displaying the white color, the black particles 1300cannot be moved to the upper inner surface so that the display colorbecomes the gray color. As a result, the display contrast is reduced.

If the CV value of the outer diameters of the microcapsules 40 issmaller than the lower limit value noted above, a structure of themicrocapsules 40 becomes a close-packed structure in a microcapsulecoating material obtained by mixing the binder 41 and the microcapsules40. Therefore, flowability of the microcapsule coating material islowered so that it becomes difficult that the microcapsule coatingmaterial is applied onto the base substrate 12.

The standard deviation (σ) of the outer diameters of the microcapsules40 is preferably 4 μm or less, more preferably 3 μm or less, and evenmore preferably 2 μm or less. It is preferred that a lower limit valueof the standard deviation (σ) of the outer diameters of themicrocapsules 40 is 0.6 μm.

If the standard deviation (σ) of the outer diameters of themicrocapsules 40 exceeds the upper limit value noted above, the shapesof the relative large microcapsules 40 become partially flattened, sothat it becomes difficult for the contact particles 50 to move along theinner surface of the capsule body 401.

As described above, the display color of the display device 20 becomesthe gray color as shown in FIG. 22. That is, if the white color is to bedisplayed after displaying the black color, the black particles 1300which are the contact particles 50 being into contact with (attachingto) the upper inner surface (flat surface) remain to the upper innersurface. As a result, the display color of the display device 20 becomesthe gray color.

On the contrary, although not shown in draws, if the black color is tobe displayed after displaying the white color, the black particles 1300cannot be moved to the upper flat inner surface so that the displaycolor becomes the gray color. As a result, the display contrast isreduced.

If the standard deviation (σ) of the outer diameters of themicrocapsules 40 is smaller than the lower limit value noted above, thestructure of the microcapsules 40 becomes the close-packed structure inthe microcapsule coating material obtained by mixing the binder 41 andthe microcapsules 40. Therefore, the flowability of the microcapsulecoating material is lowered so that it becomes difficult that themicrocapsule coating material is applied onto the base substrate 12.

When viewed from a side surface of the display device 20 (a verticaldirection to the sheet of FIG. 1), an average roundness R of themicrocapsules 40 represented by the following formula (I) is preferablyin the range of 0.88 to 1, more preferably in the range of 0.90 to 1,and even more preferably in the range of 0.90 to 0.99.

If the average roundness R is smaller than the lower limit value notedabove, it becomes difficult for the contact particles 50 to move alongthe inner surface of the capsule body 401, depending on otherconditions. As a result, the display contrast is reduced.

R=L₀/L₁  (I)

L₁ (μm) represents a circumference of a projected image of themicrocapsule 40 that is a subject of measurement, and L₀ (μm) representsa circumference of a perfect circle (a geometrically perfect circle)having the same area as that of the projected image of the microcapsule40 that is a subject of measurement.

As will be set forth later, the display device 20 is generallymanufactured by interposing the adhesive agent layer 8 between thecircuit board 22 and the display sheet 21 and bonding the circuit board22 and the display sheet 21 together under that state. The bonding isperformed in a state that the circuit board 22 and the display sheet 21are kept in close proximity to each other. Pressure is applied tobetween the circuit board 22 and the display sheet 21 in order to bringthem into close proximity to each other.

Further, when the display device 20 of the present invention isincorporated into an electronic paper that requires flexibility,flexural deformation occurs in the display device 20 each time theelectronic paper is flexed. Every time the flexural deformation occurs,pressure is applied to between the circuit board 22 and the displaysheet 21.

The microcapsules 40 have strength great enough to keep a sphericalshape between the second electrode 4 and the adhesive agent layer 8 evenwhen the pressure is applied to between the circuit board 22 and thedisplay sheet 21. This makes it possible to increase pressure resistanceand bleed resistance of the microcapsules 40, thereby ensuring that thedisplay device 20 is stably operated for an extended period of time.

The term “pressure resistance of the microcapsules 40” used hereinrefers to a property with which the microcapsules 40 resist the pressureapplied thereto without being crushed. The term “bleed resistance of themicrocapsules 40” used herein refers to a property with which theliquid-phase dispersion medium 6 contained in the microcapsules 40 iskept against dissipation to the outside.

Next, a description will be made on a principle of displayinginformation (images) in the display device 20 based on FIGS. 9A to 9E.

FIG. 9A shows a state that the capsule body 401 of the spherical shellshape is uniformly positively charged. The state can be referred to as astate that the capsule body 401 is electrically charged by the staticelectricity. In this sate, no electrical fields are generated inside thecapsule body 401, which is obvious from Gauss law.

This may be interpreted as that the sum of the electrical fields becomeszero by compensating the electrical fields, which are made by theelectrical charges on the capsule body 401, to each other at all pointson the capsule body 401. Therefore, even if a dispersion liquidcontaining particles having negative zeta potential (negatively-chargedparticles) is introduced into the capsule body 401, the particlescontained in the dispersion liquid are not attracted to the innersurface of the capsule body 401 by the static electricity.

In this regard, JP-A 2006-343782 discloses the configuration of thedisplay device as described above. In the configuration of the displaydevice, particles inside the capsule body are not attracted to the innersurface of the capsule body by the principle (theory) described above.

In FIG. 9A, the particles contained in the dispersion liquid arenegatively charged. In this case, if the particles are surrounded bycounter ions having the opposite polarity as that of the particles,namely, positive ions, the dispersion liquid are electrically neutralwhen considering at the whole dispersion liquid. In other words, the sumof the electrical charges inside the capsule body 401 is zero (netcharges do not exist inside the capsule body 401).

FIG. 9B shows not a mechanism by the static electricity but a mechanismby dissociation of salts as a mechanism of electrically charging thecapsule body 401. In a system in which a liquid involves, that is, inthe mechanism by the dissociation of the salts, the capsule body 401 isdominantly electrically charged by the mechanism.

In FIG. 9B, the salts are dissociated to the ions including cations andanions, and then the cations (positive ions) are preferentially taken(adsorbed) in the capsule body 401, and the anions (negative ions) aresuspended in water or the binder which surrounds the capsule body 401.FIG. 9B shows such a phenomenon.

In a method of manufacturing microcapsules filled with a nonaqueousliquid, it is general that a nonaqueous solvent (dispersion medium) isemulsified in water, and therefore O/W type emulsion is made. Therefore,the ions dissociated in water are selectively adsorbed to the capsulebody 401 as shown in FIG. 9B so that the whole capsule body 401 iselectrically charged with ease.

However, in this case, effective electrical fields to attract theparticles to the inner surface of the capsule body 401 are not generatedinside the capsule body 401. The reason is the same as that described inthe explanation in FIG. 9A as described above. That is, the reason isthat the sum of the electrical fields becomes zero by compensating theelectrical fields, which are made by the electrical charges on thecapsule body 401, to each other.

Therefore, even if the particles having negative zeta potential isintroduced into the capsule body 401, the particles are not attracted tothe inner surface of the capsule body 401 by the static electricity.

FIG. 9C shows that the salts are dissociated to the ions including thecations and the anions, and then the cations are preferentially taken(adsorbed) in the capsule body 401 like FIG. 9B. In this regard, it isto be noted that the dissociation to the ions occurs in the liquidincluded in the capsule body 401, and therefore the anions are includedin the capsule body 401.

In this configuration, an electrical double layer is formed on aboundary between the liquid included in the capsule body 401 and thecapsule body 401. As a result, the electrical fields are generatedinside the capsule body 401.

Therefore, if the particles having negative zeta potential is introducedinto the capsule body 401, the particles are moved toward the innersurface of the capsule body 401, and then the particles are in contactwith (adhere to) the inner surface thereof.

Apparently, the particles look like that the particles are absorbed tothe inner surface of the capsule body 401 by the static electricity(attractive force) between the particles and the cations which areadsorbed to the inner surface of the capsule body 401. However, asdescribed above, the sum of the electrical fields which are made by theelectrical charges on the capsule body 401 is zero. Therefore, force(biasing force) of allowing the particles to adhere to the inner surfaceof the capsule body 401 is obtained due to the anions which aredispersed in the liquid contained in the capsule body 401.

In other words, the particles are not attracted by the capsule body 401,but are pushed (adsorbed) to the inner surface of the capsule body 401by the repelling force (repulsive force) occurring due to the staticelectricity between the anions and the particles.

As shown in FIG. 9D, the capsule body 401 are not electrically charged,and the liquid included in the capsule body 401 has electrical charges.Even in such a case, the effective electrical fields are generatedinside the capsule body 401 as the case shown in FIG. 9C. In a casewhere the electrical charges of the liquid included in the capsule body401 are negative as shown in FIG. 9D, if the particles having negativezeta potential is introduced into the capsule body 401, the particlesare moved toward the inner surface of the capsule body 401, and then theparticles are in contact with (adhere to) the inner surface thereof.

In this way, in order to bring the particles into contact with the innersurface of the capsule body 401, the sum of the electrical chargesinside the capsule body 401 is not zero, and it is required that thepolarity of the electrical charges is the same as that of the particles.

Therefore, in a case where the salts contained in the liquid in thecapsule body 401 are dissociated, and the anions and cations remaininside the capsule body 401, the sum of the electrical charges in thecapsule body 401 becomes zero. Therefore, force, in which the particlesare in contact with the inner surface of the capsule body 401 and whichis needed to the present invention, is not generated.

However, as shown in FIG. 9E, in a case where either the cations or theanions which are dissociated in the capsule body 401 are selectivelyspread outside the capsule body 401, the sum of the electrical chargesin the capsule body 401 becomes non-zero. Therefore, the effectiveelectrical fields are generated inside the capsule body 401.

Of course, salts which have existed outside the capsule body 401 aredissociated, thereby generating the anions and the cations. FIG. 9Eshows a case where the anions are selectively spread inside the capsulebody 401, and therefore the anions are in equilibrium with the cationsoutside the capsule body 401. In such a case, the effective electricalfields are generated inside the capsule body 401. Since the capsule body401 is generally formed by a polymer, it is possible for the ions tospread inside or outside the capsule body 401 without large faults.

As described above, the microcapsules filled with the nonaqueous liquidare manufactured through the step of emulsifying the liquid in water. Ina case where salts, which are dissociated to cations having highhydrophilic property and anions having high hydrophobic property, areintroduced into the microcapsules in this step, an equilibrium conditionis obtained as shown in FIG. 9E. In this case, the whole microcapsule isobserved so as to be negatively charged in water.

As described above, the electrical fields inside the capsule body 401needed to the display device 20 operating with the electro-crawlingmethod according to the present invention are not generated by theelectrical charges on the capsule body 401.

In other words, in a case where the net charges of which polarity is thesame as that of the particles exist inside the capsule body 401, theelectrical fields are generated. Such electrical fields developelectrostatic force to act on pushing (pressing) the particles to theinner surface of the capsule body 401.

Next, a description will be made on a concrete (first to fourth)configuration examples based on FIGS. 10 to 13. In this description, thecolored particles 50 will be described as black particles 51.

First, as shown in FIG. 14, in a conventional display device, counterions (cations) exist around the negatively-charged black particles 51 inthe microcapsule, and therefore an electrically-neutral state ismaintained in the microcapsule. This electrically-neutral state isrepresented by FIG. 14. FIG. 14 shows that a number of the anionsadsorbing to the black particles 51 is the same as that of the counterions.

In this case, electrical fields which are made by the electrical chargesof the black particles 51 and act on among the black particles 51 areblocked by electrical fields which are made by the electrical charges ofthe counter ions. As a result, the electrical fields which are made bythe electrical charges of the black particles 51 and the electricalfields which are made by the electrical charges of the counter ions arecompensated to each other.

Therefore, repulsive force does not act on among the black particles 51except for a case where the black particles approach to each other by adistance of a micro level. Consequently, a state in which the blackparticles 51 are dispersed in the liquid filled in the microcapsule 40is maintained as shown in FIG. 14.

In the first configuration example shown in FIG. 10, the black particles51 are in contact with (adhere to) the inner surface of the capsule body401 by introducing anions and cations (which are represented by thesymbol “−” or “+” in the symbol “∘”, respectively), which are derivedfrom another kind of salts, in addition to anions and cations (which arerepresented by the symbol “−” or “+” in the symbol “□”, respectively),which are due to the charge of the black particles 51, in themicrocapsule 40.

The cations (which are represented by the symbol “+” in the symbol “∘”),which are derived from another kind of salts, are taken into the capsulebody 401 in itself. The anions (which are represented by the symbol “−”in the symbol “∘”), which are derived from another kind of salts, remainin the liquid included in the capsule body 401.

The effective electrical fields are generated in the capsule body 401due to the negative net charges, namely the charges of the anions whichare dispersed in the liquid included in the capsule body 401. Therefore,the black particles 51 are pushed to the inner surface of the capsulebody 401.

In this regard, it is to be noted that the dispersion particles (whiteparticles) 5 of which color (color hue) is different from the blackcolor are omitted in FIG. 10 (and FIGS. 11 to 13 alike). The dispersionparticles are not electrically charged or electrically charged in theopposite polarity (positive) as that of the black particles 51.Therefore, the dispersion particles 5 are maintained in a state ofdispersing within the capsule body 401.

Depending on distribution of the ions in the liquid included in themicrocapsule 40, the dispersion particles 5 are positioned in theneighborhood of the black particles 51 held to the inner surface of thecapsule body 401, far from the inner surface of the capsule body 401, orthe like. In this way, the dispersion particles 5 are distributed invarious kinds of states.

In the second configuration example shown in FIG. 11, cations (which arerepresented by the symbol “+” in the symbol “∘”), which are derived fromanother kind of salts, are diffused in the binder 41. Anions (which arerepresented by the symbol “−” in the symbol “∘”), which are derived fromanother kind of salts, remain in the liquid included in the capsule body401. This makes it possible to exit the negative net charges inside thecapsule body 401.

As the first configuration example shown in FIG. 10, the effectiveelectrical fields are generated in the capsule body 401 due to thenegative net charges, namely the charges of the anions which aredispersed in the liquid included in the capsule body 401. Therefore, theblack particles 51 are pushed to the inner surface of the capsule body401.

In the third and fourth configuration examples shown in FIGS. 12 and 13,ions (cations and anions), which are derived from another kind of salts,are not needed, respectively. In other words, only an ion pair which isinvolved to the black particles 51 to be electrically charged is needed.

Such an ion pair includes anions which are represented by the symbol “−”in the symbol “□” and cations which are represented by the symbol “+” inthe symbol “□”. The anions are selectively adsorbed to the blackparticles 51. As a result, the black particles 51 are negativelycharged.

Generally, an electrically-neutral state is maintained by allowing thecations (counter ion) to exist around the black particles 51. However,in the third configuration example shown in FIG. 12, parts of thecations are taken into the capsule body 401 in itself. As a result,negative net charges exist inside the capsule body 401. The effectiveelectrical fields are generated inside the capsule body 401 due to thenegative net charges, and therefore the black particles 51 are pushed tothe inner surface of the capsule body 401.

This may be interpreted as that the repulsive force occurring due to theelectrostatic force acts on among the black particles 51, as a result,the black particles 51 are pushed to the inner surface of the capsulebody 401 by repelling to each other.

In the fourth configuration example shown in FIG. 13, only the ion pairwhich is involved to the black particles 51 to be electrically chargedis needed. Such an ion pair includes anions which are represented by thesymbol “−” in the symbol “□” and cations which are represented by thesymbol “+” in the symbol “□”. Parts of the cations are taken in thebinder 41.

As the third configuration example shown in FIG. 12, effectiveelectrical fields are generated inside the capsule body 401 due to thenegative net charges existing inside the capsule body 401. Therefore,the black particles 51 are pushed to the inner surface of the capsulebody 401.

2. Operating Method of Display Device

Such a display device 20 is operated as follows.

Hereinafter, a method of operating the display device 20 will bedescribed with reference to FIG. 6. The following description will bemade based on a representative instance wherein the contact particles 50are negatively charged, the negative net charges exist inside thecapsule body 401, and wherein a state that the contact particles 50 arepositioned near the first electrodes 3 (namely, a state that the whitecolor is displayed) is set as an initial state.

When displaying the white color, an electrical voltage is applied tobetween the first electrodes 3 and the second electrode 4 so that thefirst electrodes 3 can be in a positive potential with respect to thesecond electrode 4. For the purpose of reliability, it is preferred thatthe electrical voltage is applied for a time long enough to allow thecontact particles 50 to move from the second electrode 4 to the firstelectrodes 3.

As a consequence, the contact particles 50 are moved along the innersurface of the capsule body 401 toward the first electrodes 3 whilemaintaining the contact state until they are stopped near the firstelectrodes 3. On the other hand, the dispersion particles 5 aremaintained in a state of dispersing into the liquid-phase dispersionmedium 6.

Therefore, a state in that the dispersion particles 5 and theliquid-phase dispersion medium 6 (liquid) included in the capsule body401 are not covered with the contact particles 50 at all is shown asviewed from the display surface side of the display device 20. That is,the state in that the contact particles 50 are not positioned near thesecond electrode 4 is shown as viewed from the display surface side ofthe display device 20 (most left drawings in FIG. 6A to 6C). Therefore,the ratio (S2/S1) becomes 0, thereby displaying the white color.

When displaying the black color, an electrical voltage is applied tobetween the first electrodes 3 and the second electrode 4 so that thefirst electrodes 3 can be in a negative potential with respect to thesecond electrode 4. For the purpose of reliability, it is preferred thatthe electrical voltage is applied for a time long enough to allow thecontact particles 50 to move from the first electrodes 3 to the secondelectrode 4.

Consequently, the contact particles 50 are moved along the inner surfaceof the capsule body 401 toward the second electrode 4 maintaining thecontact state until they are stopped near the second electrode 4. On theother hand, the dispersion particles 5 are maintained in a state ofdispersing into the liquid-phase dispersion medium 6.

Therefore, a state in that all the dispersion particles 5 and theliquid-phase dispersion medium 6 (liquid) included in the capsule body401 are covered with the contact particles 50 is shown as viewed fromthe display surface side of the display device 20.

That is, the state in that the contact particles 50 are positioned nearthe second electrode 4 is shown as viewed from the display surface sideof the display device 20 (most right drawings in FIG. 6A to 6C).Therefore, the ratio (S2/S1) becomes 1, thereby displaying the blackcolor.

When displaying the gray color as the intermediate tone, the displaydevice 20 is first restored to the initial state as is the case whendisplaying the white color. Thereafter, the electrical voltage isapplied to between the first electrodes 3 and the second electrode 4 sothat the first electrodes 3 can be in a negative potential with respectto the second electrode 4.

In this case, analytical curves (e.g., arithmetic expressions, tables,etc.) showing a correlation between a gray color of different gradations(respective intermediate tones) and a voltage application time has beenempirically found in advance and stored in a storage means not shown inthe drawings.

Based on these analytical curves, a control means not shown in thedrawings calculates a voltage application time required in obtaining thegray color of the desired gradation (the desired intermediate tone) andapplies an electrical voltage for the voltage application time thuscalculated.

Consequently, the contact particles 50 are moved along the inner surfaceof the capsule body 401 toward the second electrode 4 maintaining thecontact state until they are stopped at a predetermined position.

On the other hand, the dispersion particles 5 are maintained in a stateof dispersing into the liquid-phase dispersion medium 6. Therefore, astate in that a circumference portion of the dispersion particles 5 andthe liquid-phase dispersion medium 6 (liquid) included in the capsulebody 401 are covered with the contact particles 50 is shown as viewedfrom the display surface side of the display device 20.

That is, a state in that the contact particles 50 are positioned nearthe second electrode 4 and at the circumference portion is shown asviewed from the display surface side of the display device 20 (twodrawings between the most left drawing and the most right drawing ineach of FIG. 6A to 6C). Therefore, the ratio (S2/S1) becomes apredetermined value which is larger than 0 and lower than 1, therebydisplaying the gray color of the desired gradation.

For example, in the second display example from the left side ofdrawings in each of FIGS. 6A to 6C, the relative-light gray color (nearwhite color) is displayed. On the other hand, in the third displayexample from the left side of the drawings in each of FIGS. 6A to 6C,the relative-dark gray color (near black color) is displayed.

The display of each of the colors and a combination thereof makes itpossible to display desired information (desired images).

It goes without saying that other colored particles (e.g., cyan (C)particles, magenta (M) particles, yellow (Y) particles, red (R)particles, green (G) particles and blue (B) particles) may be used asthe contact particles 50. In this case, it is possible to displayarbitrary intermediate tones between those colors and the white color inthe same manner as described above.

In this case, it becomes possible to provide color display and fullcolor display. Furthermore, colored particles of which hue is differentfrom that of the contact particles 50 may be used as the dispersionparticles 5.

3. Method of Manufacturing Display Device

The display device 20 described above can be manufactured in thefollowing manner. Hereinafter, a method of manufacturing the displaydevice 20 will be described with reference to FIGS. 7A to 7D and 8E to8G.

The method of manufacturing the display device 20 illustrated in FIGS.7A to 7D and 8E to 8G includes a microcapsule production step [A1] forproducing the microcapsules 40, a microcapsule coating materialpreparation step [A2] for preparing a microcapsule coating material(microcapsule dispersion liquid) containing the microcapsules 40, amicrocapsule-containing layer formation step [A3] for forming themicrocapsule-containing layer 400 containing the microcapsules 40 on onesurface of the base substrate 12, an adhesive agent layer formation step[A4] for forming the adhesive agent layer 8 on an opposite surface ofthe microcapsule-containing layer 400 from the base substrate 12, abonding step [A5] for bringing the opposite substrate 11 into contactwith an opposite surface of the adhesive agent layer 8 from themicrocapsule-containing layer 400 and bonding the adhesive agent layer 8and the opposite substrate 11 together, and a sealing step [A6] forforming the sealing portion 7.

The microcapsule production step [A1], the microcapsule coating materialpreparation step [A2] and the microcapsule-containing layer formationstep [A3] constitute a microcapsule-containing layer formation step inthe method of manufacturing the display device according to the presentinvention.

A step for producing the base substrate 12 to be prepared in themicrocapsule-containing layer formation step [A3] includes a secondelectrode formation step for forming the second electrode 4 on the lowersurface of the base portion 2.

A step for producing the circuit board 22 to be prepared in the bondingstep [A5] includes a first electrode formation step for forming thefirst electrodes 3 on the upper surface of the base portion 1.

The second electrode formation step and the first electrode formationstep constitute an electrode formation step in the method ofmanufacturing the display device according to the present invention.Hereinafter, a description will be made on the respective steps.

[A1] Microcapsule 40 Production Step

[A1-1] Formation of First Capsule Layer 402

First obtained are microcapsules in which the dispersion liquid 10 andthe contact particles 50 are encapsulated into the first capsule layer402. For the purpose of convenience in the description, thesemicrocapsules will be referred to as “pre-microcapsules (microcapsuleprecursors)” hereinbelow.

The first capsule layer 402 can be formed by various kinds of amicrocapsule production method, using a controlled liquid composed ofthe dispersion liquid 10 and the contact particles 50 as a corematerial.

The microcapsule production method (a method of encapsulating thecontrolled liquid into the first capsule layer 402) is not particularlylimited to a specific type, but examples of the microcapsule productionmethod include an interfacial polymerization method, an in-situpolymerization method, a phase separation method (or a coacervationmethod), an interfacial sedimentation method and a spray drying method.These microcapsule production methods may be suitably selected dependingon the constituent material of the first capsule layer 402 or otherconditions.

In this regard, a step of providing the net charges of which polarity isthe same as that of the contact particles 50 in the first capsule layer402 is not performed during the process of forming the first capsulelayer 402. Instead, the step is performed after the formation of thefirst capsule layer 402.

If the first capsule layer 402 is electrically charged during theprocess of forming the same, the contact particles 50 will be pushed toand embedded in (or fixed to) the first capsule layer 402 due to theelectrostatic force therebetween. Such a problem can be surely avoidedby not electrically charging the first capsule layer 402.

The pre-microcapsules having a uniform size can be obtained by using,e.g., a sieving method, a filtering method or a specific gravitydifference sorting method.

[A1-2] Formation of Second Capsule Layer 403

Next, the second capsule layer 403 is formed on the outer surface ofeach of the pre-microcapsules (the first capsule layer 402) obtained inthe step [A1-1], thereby producing the microcapsules 40 which includethe dispersion liquid 10 and the contact particles 50 therein.

The second capsule layer 403 can be formed by, e.g., gradually adding aresin prepolymer to a capsule dispersion liquid in which thepre-microcapsules are dispersed in an aqueous medium and causing acondensation reaction to the prepolymer adsorbed to the outer surfacesof the pre-microcapsules.

By doing so, the second capsule layer 403 is formed on the outer surfaceof each of the pre-microcapsules, thus producing the microcapsules 40containing the dispersion liquid 10 and the contact particles 50.

When forming the second capsule layer 403, the net charges of whichpolarity is the same as that of the contact particles 50 exist withinthe capsule body (first capsule layer 402) 401 (step of electricallycharging the capsule body 401).

In this case, the constituent material (the combination of components ofthe constituent material), the mixing ratio of the components and thevarious forming conditions of each of the first capsule layer 402 andthe second capsule layer 403 are suitably set depending on thedispersion liquid 10 used. Further, charges of which polarity is thesame as that of the contact particles 50 are provided in the dispersionliquid 10.

By doing so, the net charges of which polarity is the same as that ofthe contact particles 50 exist within the capsule body 401, that is, thefirst capsule layer 402, while adjusting the charge amount and thecharge density thereof. Through this charging step, the contactparticles 50 are in contact with the inner surface of the capsule body401 due to the electrostatic force therebetween.

In this regard, it is needless to say that the method of providing(existing) the net charges having the same polarity as that of thecontact particles 50 inside the capsule body 401 is not limited to theabove method.

The microcapsules 40 having a uniform size, that is, the microcapsules40 in which the average value, the CV value, and the standard deviationof the outer diameters fall within the above noted range, can beobtained by using, e.g., a sieving method, a filtering method or aspecific gravity difference sorting method.

As set forth above, in the microcapsule production step [A1] of themethod of this embodiment, the charging step for electrically chargingthe capsule body 401 is performed after forming the first capsule layer402 that constitutes an inner portion of the capsule body 401.

As described above, a method of adjusting the CV value and the standarddeviation of the outer diameters of the microcapsules 40 include variouskinds of methods, e.g., a sieving method, a filtering method, a microemulsifying method using a micro reactor, an inkjet method and aspecific gravity difference sorting method.

In particular, the micro emulsifying method or the inkjet method ispreferably used. The inkjet method is a method of ejecting a preparingliquid constituted of the dispersion liquid 10 and the contact particles50 from nozzles of a droplet ejection head. The use of these methodsmakes it possible to produce the microcapsules 40 having a small CVvalue and a small standard deviation of the outer diameters thereofwithout the use of sieving method or the like.

In this regard, it needless to say that the sieving method, thefiltering method, and the specific gravity difference sorting method maybe used at the same time with the micro emulsifying method or the inkjetmethod.

Next, an easy description will be made on a method using the microreactor.

FIG. 15 is a section view schematically showing a configuration exampleof a major part of a micro reactor 9. Hereinafter, the left side in FIG.15 will be referred to as “one end” and the right side will be referredto as “the other end” for the purpose of convenience in the description.

As shown in FIG. 15, the micro reactor 9 has a first tube (flow path)91, a second tube (flow path) 92, and a third tube (flow path) 93, whichhave a small inner diameter, respectively. The other ends of the firsttube 91 and the second tube 92 are connected to each other, and areconnected with one end of the third tube 93.

A preparing liquid constituted of the dispersion liquid 10 and thecontact particles 50 flows in the first tube 91. A liquid, which isneeded to emulsify an emulsifying agent and the like, flows in thesecond tube 92. The preparing liquid and the liquid are joined togetherat the one end of the third tube 93. At that time, the preparing liquidflows in the third tube 93 in a form of spherical droplets having apredetermined size.

If conditions such as a flow rate of the preparing liquid, a flow rateof the emulsifying agent, and the like are adjusted, the preparingliquid can be adjusted in a predetermined size. Thereafter,pre-microcapsules in which the dispersion liquid 10 and the contactparticles 50 are encapsulated in the first capsule layer 402 areobtained through predetermined steps. Then, the microcapsules 40 areobtained as described above.

According to the method, it is possible to produce microcapsules 40having a small CV value and a small standard deviation of the outerdiameters without classifying the microcapsules 40 using the filteringmethod and the like. Therefore, it is possible to obtain themicrocapsules 40 with a high yield.

Next, an easy description will be made on the inkjet method. Thepreparing liquid constituted of the dispersion liquid 10 and the contactparticles 50 is introduced into a droplet ejection head provided with adroplet ejection apparatus which is placed under the atmosphere. Next,droplets of the preparing liquid are ejected from nozzles of the dropletejection head to a solution in which the emulsifying agent is dissolved.

This makes it possible to obtain droplets of the preparing liquid in aform of spherical droplets having a predetermined size in the solution.An ejection rate of the droplets is preferably 8 m/s or less, and morepreferably 4 m/s or less. By setting the ejection rate of the dropletsas described above, it is possible to prevent (or suppress) satellitesfrom being generated.

[A2] Microcapsule Coating Material Preparation Step

Next, the binder 41 and a solvent are prepared, and then this binder 41and the solvent are mixed with the microcapsules 40 produced in the step[A1] to thereby obtain a microcapsule coating material.

A mixing ratio of the binder 41 and the microcapsules 40 produced in thestep [A1] is such that an amount of the binder 41 is preferably in therange of about 20 to 45 vol % with respect to a total amount of themicrocapsules 40 and the binder 41.

If the amount of the binder 41 is smaller than the lower limit valuenoted above, when the microcapsule coating material is dried, there is afear that spaces (gaps) are formed among the microcapsules 40, andtherefore the microcapsules 40 are deformed under its own weight or in acircuit board 22 bonding step (A5) which will be described lateraccording to other conditions.

If the amount of the binder 41 exceeds the upper limit value notedabove, there is a fear that large gaps among the microcapsules 40 areobtained according to other conditions, and therefore the displayperformance such as the display contrast and the like is lowered.

An amount of the microcapsules 40 contained in the microcapsule coatingmaterial is preferably in the range of about 30 to 60 wt %, and morepreferably in the range of about 40 to 60 wt %.

If the amount of the microcapsules 40 is set to fall within theabove-noted range, there is provided a great advantage in that themicrocapsules 40 can be moved (or rearranged) within themicrocapsule-containing layer 400 in such a manner as not to overlap oneanother in a thickness direction thereof (namely, in such a manner as toform a single layer).

[A3] Microcapsule-Containing Layer 400 Formation Step

Next, the base substrate 12 is prepared as illustrated in FIG. 7A. Then,the microcapsule coating material prepared in the step [A2] is appliedon the base substrate 12 as illustrated in FIG. 7B.

A method of applying the microcapsule coating material is notparticularly limited to a specific type. As the method, various kinds ofapplication methods such as an applicator method, a bar coater method, adie coater method, an air knife coater method, a kiss coater method anda gravure coater method can be used.

If necessary, the microcapsule coating material is leveled so that athickness (a quantity) thereof can become uniform across the basesubstrate 12, preferably so that the microcapsules 40 can be arrangedside by side (in a single layer) without overlapping one another in athickness direction of a liquid coat composed of the microcapsulecoating material.

The leveling operation can be performed by, e.g., horizontally moving asqueegee (a plate-like jig) above the base substrate 12 to sweep themicrocapsules 40 as illustrated in FIG. 7C. Thus, themicrocapsule-containing layer 400 is formed and the display sheet 21 isobtained as illustrated in FIG. 7D. In this regard, the microcapsulecoating material is introduced to a head of the die coater describedabove, thereby enabling the microcapsule coating material to coat.

[A4] Adhesive Agent Layer 8 Formation Step

Next, the adhesive agent layer 8 is formed on themicrocapsule-containing layer 400 as illustrated in FIG. 8E.

This step can be performed by, e.g., arranging an adhesive agent layer 8having a sheet shape on the microcapsule-containing layer 400 using anovercoat method, a transfer method or the like.

[A5] Circuit Board 22 Bonding Step

Next, as illustrated in FIG. 8F, the circuit board 22 preparedseparately is laminated on the adhesive agent layer 8 so that the firstelectrodes 3 can come into contact with the adhesive agent layer 8. Bydoing so, the display sheet 21 and the circuit board 22 are bondedtogether through the adhesive agent layer 8.

At this time, an arrangement density of the microcapsules 40 in themicrocapsule-containing layer 400 can be made uniform due to weight ofthe adhesive agent layer 8 and the circuit board 22 or by pressing thecircuit board 22 and the display sheet 21 toward each other (by reducingthe thickness of the microcapsule-containing layer 400).

When pressing the circuit board 22 and the display sheet 21 toward eachother, magnitude of the pressure applied thereto is usually set equal toabout 0.05 to 0.6 MPa.

However, in this display sheet 21 (this display device 20), the pressureis set to ensure that the microcapsules 40 contained in themicrocapsule-containing layer 400 can be kept in a generally sphericalshape without being compressed (pressed) in an up-and-down directionthereof, even if the microcapsule-containing layer 400 is pinched by thesecond electrode 4 and the adhesive agent layer 8 in a state that thepressure of the above noted magnitude is applied to between the circuitboard 22 and the display sheet 21.

Consequently, it is possible to surely prevent collapse of themicrocapsules 40 and dissipation of the dispersion liquid 10 and thecontact particles 50, which would otherwise be caused by the pressureapplied to between the circuit board 22 and the display sheet 21.Furthermore, it is possible for the contact particles 50 to smoothly andreliably move along the inner surface of the capsule body 401.

[A6] Sealing Step

Next, as illustrated in FIG. 8G, the sealing portion 7 is formed alongthe edges of the display sheet 21 and the circuit board 22.

The sealing portion 7 can be formed by supplying a sealing portionformation material to between the display sheet 21 (the base portion 2)and the circuit board 22 (the base portion 1) along the edges thereofthrough use of, e.g., a dispenser, and then solidifying or curing thesealing portion formation material.

The display device 20 is manufactured through the steps described above.

The adhesive agent layer 8 may be arranged only on the circuit board 22or on both of the circuit board 22 and the display sheet 21 to therebybond the circuit board 22 and the display sheet 21 together.

It is preferred that the adhesive agent layer 8 having the sheet shapeis arranged on the microcapsule-containing layer 400 by bending thesame, bringing one end portion thereof into contact withmicrocapsule-containing layer 400 and allowing the same to progressivelycome into contact with the microcapsule-containing layer 400 from oneend toward the other end.

By doing so, it is possible to prevent air bubbles from being leftbetween the microcapsule-containing layer 400 and the adhesive agentlayer 8, and to reliably rearrange the microcapsules 40.

The adhesive agent layer 8 may be omitted, and the display sheet 21 andthe circuit board 22 may be bonded together using other methods. As oneexample of other methods, the display sheet 21 and the circuit board 22may be bonded together by means of the binder 41.

According to the display device 20 described above, the contactparticles 50 are always in contact with any region on the inner surfaceof the capsule body 401. The contact particles 50 are reliably movedalong the inner surface of the capsule body 401 while maintaining thecontact state. Further, the contact particles 50 and the dispersionparticles 5 are not adsorbed to each other. Therefore, it is possible toeasily and reliably obtain the intermediate tone.

In addition, since the contact particles 50 are in contact with theinner surface of the capsule body 401 even at the stoppage of theapplication of the electrical voltage to between the first electrodes 3and the second electrode 4, it is possible to reliably maintain theindividual colors including the intermediate tone. This ensures that thedisplay content (the image) is stably maintained with no deteriorationof its display state even at the stoppage of the voltage application.

Owing to the fact that the contact particles 50 are in contact with theinner surface of the capsule body 401 and further that the contactparticles 50 and the dispersion particles 5 are not adsorbed to eachother, it is possible to exhibit high display contrast and to improvechromatic purity.

Seeing that the contact particles 50 are moved along the inner surfaceof the capsule body 401 while maintaining the contact state, it ispossible to reliably move the contact particles 50 with relatively weakelectrical fields, thereby reducing power consumption of the displaydevice 20.

Furthermore, seeing that the CV value of the outer diameters of themicrocapsules 40 is small, the shape of each of the microcapsules 40does not become flattened, but a spherical shape. This makes it possiblefor the contact particles 50 to reliably move along the inner surface ofthe capsule body 401 while maintaining the contact state when thecontact particles 50 are moved. Therefore, it is possible to reliablydisplay respective colors including the intermediate tone and exhibithigh display contrast.

Seeing that the average value of the outer diameters of themicrocapsules 40 falls within the above noted range, it is difficult forthe microcapsule body 401 to deform. Further, relatively large amountsof the contact particles 50 and the dispersion particles 5 can beincluded in the capsule body 401. This makes it possible for the whiteparticles to improve property of concealing the black particles when thewhite display. As a result, the white color is displayed clearly,thereby exhibiting high display contrast.

In a conventional display device operating with an electrophoresismethod, when dispersibility of black particles and white particlescontained in an electrophoretic dispersion liquid is improved, it ispossible to rapidly switch (change) a display color to the other displaycolor. However, in a display state, since the black particles and thewhite particles are moved with ease, it is impossible to maintain adisplay state of a predetermined color.

On the other hand, when the dispersibility of the black particles andthe white particles contained in the electrophoretic dispersion liquidis lowered, in the display state, it is difficult that the blackparticles and the white particles are moved. Although this makes itpossible to maintain the display state of the predetermined color forrelatively a long period of time, it is impossible to rapidly switch(change) a display color to the other display color.

According to the display device of present invention, seeing that thecontact particles 50 are moved along the inner surface of the capsulebody 401 while maintaining the contact state, even if dispersability ofthe dispersion particles 5 contained in the dispersion liquid 10 isimproved, it is possible to reliably maintain the display state ofrespective colors including the intermediate tone and rapidly switch thedisplay color to the other display color.

This display device 20 is a so-called microcapsule type and thereforecan be manufactured more easily and reliably than what is called amicrocup type display device.

Second Embodiment

Hereinafter, a second embodiment will be described, with emphasis placedon the differing points from the first embodiment but with nodescription made on the same matters.

In a method of manufacturing a display device 20 of the secondembodiment, the capsule body 401 is not electrically charged whenforming the same. After the capsule body 401 has been formed in itsentirety, namely after the microcapsule production step [A1] has beencompleted, a charging step for providing (existing) the net charges withthe same polarity as that of the contact particles 50 inside the capsulebody 401 through the binder is performed in the microcapsule coatingmaterial preparation step [A2].

In this case, a specified amount of positive or negative charging agentmay be added to the binder 41 depending on the polarity of the contactparticles 50. This makes it possible to adjust the charge amount and thecharge density of the capsule body 401 while providing the net chargeswith the same polarity as that of the contact particles 50 inside thecapsule body 401. In this regard, it is to be noted that the binder 41may be or may not be electrically charged.

The display device 20 thus constructed can exercise the sameadvantageous effects as those of the display device 20 of the firstembodiment.

Third Embodiment

Hereinafter, a third embodiment will be described, with emphasis placedon the differing points from the first embodiment but with nodescription made on the same matters.

FIGS. 16A and 16B are pattern diagrams for explaining another method ofmanufacturing the display device shown in FIG. 1. In the followingdescription, the upper side in FIGS. 16A and 16B will be referred to as“upper” with the lower side as “lower”, for the purpose of conveniencein the description.

The third embodiment is the same as the first embodiment except that amicrocapsule-containing layer 400 formation step (A3) is different fromthat of the first embodiment.

A microcapsule coating material in which an amount (amount ratio) of abinder 41 is relatively low is used in the microcapsule-containing layer400 formation step (A3) of the third embodiment. To be concrete, theamount of the binder 41 contained in the microcapsule coating materialis preferably in the range of about 20 to 30 vol % with respect to atotal amount of the microcapsules 40 and the binder 41.

If the amount of the binder 41 contained in the microcapsule coatingmaterial is too much, the microcapsule coating material can not beapplied onto the base substrate so that the microcapsules 40 are denselyarranged. In addition, an extra binder 41 enters into gaps between themicrocapsules 40 and the second electrode 4 or the adhesive agent layer8 (first electrodes 3). Furthermore, the microcapsules 40 are arrangedso as to overlap to each other with ease.

In this embodiment, first, by using the microcapsule coating material inwhich the amount of the binder 41 is relatively low, the microcapsulecoating material is applied onto the base substrate 12 as shown in FIG.16A, the applied microcapsule coating material is dried, and then asmoothing treatment is carried out to the dried microcapsule coatingmaterial.

This makes it possible to apply the microcapsule coating material ontothe base substrate 12 so that the microcapsules 40 are densely arranged.In addition, the microcapsules 40 can be in contact with (adhere to) thesecond electrode 4 or the adhesive agent layer 8 (first electrodes 3).Furthermore, the microcapsules 40 can be arranged in a single layermanner.

Since the amount of the binder 41 contained in the microcapsule coatingmaterial is relatively low, the entire microcapsules 40 can not becovered with the binder 41. In FIG. 16A, the lower portions of themicrocapsules 40 are covered with the binder 41.

Next, as shown in FIG. 16B, a binder liquid obtained by mixing thebinder 41 and a solvent is further applied onto the microcapsules 40,thereby providing a remaining amount of the binder 41 to be used as themicrocapsule-containing layer 400. This makes it possible to cover theentire microcapsules 40 with the binder 41. The following steps will beomitted from the description because the following steps are the same asthose of the first embodiment.

The display device 20 thus constructed can exercise the sameadvantageous effects as those of the display device 20 of the firstembodiment.

Fourth Embodiment

FIG. 17 is a vertical section view schematically showing a fourthembodiment of a display device according to the present invention. Inthe following description, the upper side in FIG. 17 will be referred toas “upper” with the lower side as “lower”, for the purpose ofconvenience in description. In FIG. 17, the microcapsule 40 is drawn ina single layer manner for easy description.

Hereinafter, the fourth embodiment will be described, with emphasisplaced on the differing points from the first embodiment but with nodescription made on the same matters.

In a display device 20 of the fourth embodiment, microcapsule 40includes a structural body 13 which is provided in the microcapsule 40so as to be spaced apart from the inner surface of the capsule body 401to a predetermined distance as a scattering body or a colored particles.

In this embodiment, an external form of the structural body 13 is asimilar figure to the shape of the capsule body 401. The structural body13 is fixed to a predetermined portion of the capsule body 401, (e.g. inFIG. 17, an opposite portion of the capsule body 401 to the displaysurface, that is a lower portion of the capsule body 401), by asupporting portion 131.

The contact particles 50 are positioned in a space (gap space) 14between an outer surface of the structural body 13 and the inner surfaceof the capsule body 401. The contact particles 50 are moved along theinner surface of the capsule body 401 while maintaining the contactstate.

In this regard, it is to be noted that the supporting portion 131 is ina shape of a small rod, does not prevent the movement of the contactparticles 50.

The structural body 13 is not particularly limited to a specific body aslong as it has a function of scattering light or a different hue fromthat of contact particles 50. Examples of such a structural body 13include: one in which at least one of particles (powder), a liquid, anda gas are encapsulated in a shell (shell); a solid body (bulk body); andthe like.

In this regard, it is to be noted that a gas such as air may be filledinto the space 14. Further, the space may be in a state of a near vacuum(substantially vacuum).

The display device 20 thus constructed can exercise the sameadvantageous effects as those of the display device 20 of the firstembodiment.

Electronic Apparatus

The display device 20 described above can be used for constituting avariety of electronic apparatuses. Hereinafter, a description will bemade on examples of an electronic apparatus of the present inventionprovided with the display device 20.

Electronic Paper

First, a description will be offered regarding an embodiment in whichthe electronic apparatus of the present invention is used in anelectronic paper.

FIG. 18 is a perspective view showing an embodiment in which theelectronic apparatus according to the present invention is used in anelectronic paper.

The electronic paper 600 shown in FIG. 18 includes a main body 601formed of a rewritable sheet having the same texture and flexibility asthat of a paper sheet, and a display unit 602 attached to the main body601. In the electronic paper 600, the display unit 602 is formed fromthe display device 20 described above.

Display Apparatus

Next, a description will be offered regarding an embodiment in which theelectronic apparatus of the present invention is used in a displayapparatus.

FIGS. 19A and 19B are section and plan views showing an embodiment inwhich the electronic apparatus according to the present invention isused in a display apparatus.

The display apparatus 800 shown in FIGS. 19A and 19B includes a mainbody portion 801 and an electronic paper 600 detachably attached to themain body portion 801. The electronic paper 600 is of the sameconfiguration as set forth above, i.e., the same configuration as shownin FIG. 18.

Formed on one lateral side (the right side in FIG. 19A) of the main bodyportion 801 is an insertion slot 805 through which the electronic paper600 can be inserted. Two pairs of conveying rollers 802 a and 802 b areprovided within the main body portion 801.

When the electronic paper 600 is inserted into the main body portion 801through the insertion slot 805, the electronic paper 600 is held withinthe main body portion 801 in a state that it is gripped by means of thepairs of conveying rollers 802 a and 802 b.

A rectangular opening 803 is formed on a display surface side (the frontside in FIG. 19B) of the main body portion 801 and a transparent glassplate 804 is fitted to the rectangular opening 803. This allows theelectronic paper 600 held within the main body portion 801 to bevisually recognized from the outside of the main body portion 801.

In other words, the display apparatus 800 has a display surface thatallows the electronic paper 600 held within the main body portion 801 tobe visually recognized through the transparent glass plate 804.

A terminal portion 806 is formed in a leading edge portion (the leftside in FIGS. 19A and 19B) of the electronic paper 600. Provided withinthe main body portion 801 is a socket 807 that makes contact with theterminal portion 806 when the electronic paper 600 is placed within themain body portion 801. A controller 808 and an operation part 809 areelectrically connected to the socket 807.

In the display apparatus 800 set forth above, the electronic paper 600is removably fitted to the main body portion 801 and is portable in astate that it is removed from the main body portion 801.

Furthermore, the electronic paper 600 of the display apparatus 800 isformed from the display device 20 described above.

In this regard, it is to be noted that the electronic apparatus of thepresent invention is not limited to the uses as described above.Examples of other uses of the electronic apparatus include a televisionset, a viewfinder type or monitor viewing type video tape recorder, acar navigation system, a pager, a personal digital assistance, anelectronic calculator, an electronic newspaper, a word processor, apersonal computer, a workstation, a picture phone, a POS terminal, adevice provided with a touch panel and the like. The display device 20of the present invention can be used in display parts of the variouskinds of electronic apparatuses described above.

While the present invention has been described hereinabove based on theillustrated embodiments, the present invention is not limited thereto.The construction of each part may be replaced by an arbitraryconstruction having the same function.

Furthermore, other arbitrary constituents or steps may be added to thepresent invention. In addition, the present invention may be embodied bycombining two or more arbitrary constituents (features) of therespective embodiments described above.

While a pair of electrodes is provided in a mutually facing relationshipin the foregoing embodiments, the present invention is not limitedthereto, but may be applied to, e.g., a construction in which a pair ofelectrodes is provided on the same substrate.

While a pair of substrates is provided in a mutually facing relationshipin the foregoing embodiments, the present invention is not limitedthereto, but may be applied to, e.g., a construction having a singlesubstrate.

While the microcapsules are arranged so as not to straddle theneighboring pixel electrodes in the foregoing embodiments, the presentinvention is not limited thereto. Alternatively, the microcapsules maybe arranged to straddle, e.g., two neighboring pixel electrodes or threeor more neighboring pixel electrodes. Such arrangement patterns may beused in combination.

EXAMPLES

Next, a description will be made on concrete examples according to thepresent invention.

1. Manufacture of Display Device

A dispersion liquid according to the following synthesis example 1 wasproduced as follows.

Synthesis Example 1

A separable flask of 300 ml volume having a rotor blade, a thermometer,and a cooling pipe was prepared. Further, copolymer (MW: 5300)constituted of dodecyl methacrylate and 2-ethylhexyl acrylate (of whichratio was 85:15) was also prepared. Furthremore, a positively-chargedcarbon black (of which charge amount was +85 μc/g) (manufactured byEvonik Degussa GmbH under the trade name of “Printex 60”) was alsoprepared as contact particles (black particles).

Next, the copolymer of 2 g, the positively-charged carbon black of 20 g,and Isoper M of 78 g were added in the separable flask. Beads of 800 g,which had 1 mmΦ (diameter) and were made of zirconia, were further addedin the separable flask to obtain a first mixture. The first mixture wasmixed at an agitating speed of 300 rpm at a temperature of 60° C. for 2hours to disperse the positively-charged carbon black (contactparticles). In this regard it is to be noted that a method of measuringa charge amount of the contact particles will be described later.

Next, Isoper M of 100 g was added in the separable flask to obtain asecond mixture, and then the second mixture was mixed. Thereafter, thebeads were separated from the second mixture to obtain a carbon blackdispersion liquid containing the carbon black of 10 wt %.

On the other hand, a separable flask of 300 ml volume having a rotorblade was prepared. Further, copolymer (MW: 6800) constituted of dodecylmethacrylate and 2-ethylhexyl acrylate, and methacryloxy propyltrimethoxy silane (of which ratio was 80:15:5) was also prepared.Furthermore, negatively-charged titanium oxide (of which charge amountwas −36 μc/g) (manufactured by ISHIHARA SANGYO KAISHYA, LTD. under thetrade name of “TIPAQUE PC-3”) was also prepared as dispersion particles(particles for scattering light).

Next, the copolymer of 5 g, the negatively-charged titanium oxide of 50g, and hexane of 100 g were added into the separable flask to obtain athird mixture. Then, the separable flask was set in an ultrasonic wavebath (manufactured by Yamato Scientific Co., Ltd. under the trade nameof “BRANSON 5210”) at a temperature 55° C. In such a sate, the thirdmixture was mixed for 2 hours while applying an ultrasonic wave thereto.

Next, the separable flask was moved (set) from the ultrasonic wave bathto a warming bath. A solvent (hexane) was removed from the third mixtureto obtain titanium oxide in a powder form. Then, the titanium oxide wastaken out from the separable flask, and then added in a vat. Thereafter,the titanium oxide was subject to a heat treatment under a temperatureof 150° C. for 5 hours.

The titanium oxide was dispersed in hexane of 100 g, and then wascentrifuged by a centrifugal settler. After the centrifuged titaniumoxide was washed three times, the washed titanium oxide was dried at atemperature of 100° C.

The thus obtained titanium oxide of 50 g and Isoper M of 50 g were addedinto a flask to obtain a fourth mixture, and then the flask was set inthe ultrasonic wave bath (manufactured by Yamato Scientific Co., Ltd.under the trade name of “BRANSON 5210”) at a temperature 55° C. In sucha sate, the fourth mixture was mixed for 2 hours while applying theultrasonic wave thereto. In this way, a titanium oxide dispersion liquidcontaining the thus obtained titanium oxide of 50 wt % was obtained.

The carbon black dispersion liquid of 6.0 g, the titanium oxidedispersion liquid of 75 g, and Isoper M of 15 g were added into amayonnaise bin of 200 ml volume to obtain a fifth mixture. The fifthmixture was mixed to obtain a dispersion liquid containing apositively-charged carbon black and a negatively-charged titanium oxide.

A display device was manufactured by using the dispersion liquid thusobtained in the Synthesis Example 1 in each of the Examples 1 to 25 andthe Comparative Examples 1 to 12.

Example 1

An aqueous solution of 120 g in which polyvinylalcohol of 6 g(manufactured by KURARAY CO., LTD. under the trade name of “KURARAYPOVAL 205”) was dissolved was added into a separable flask having a flatbottom and 500 ml volume. Next, methyl methacrylate of 10 g, glycidylmethacrylate of 2 g, tetraethyleneglycol diacrylate of 1 g, andazo-bisisobutyronitrile of 0.15 g were dissolved in the dispersionliquid containing the positively-charged carbon black and thenegatively-charged titanium oxide obtained in the Synthesis Example 1 toobtain a dispersion mixture.

Then, the dispersion mixture was added into the aqueous solution in theseparable flask while stirring it by a disper (manufactured by PRIMIXCorporation under the trade name of “ROBOMICS”) to obtain a sixthmixture. Thereafter, the sixth mixture was stirred at an agitating speedof 2000 rpm for 2 minutes, and then the agitating speed was changed from2000 rpm to 1700 rpm. Then, water of 200 g was added into the sixthmixture to obtain a suspension.

The suspension was added into a fourth-neck separable flask having athermometer and a cooling pipe. Then, a nitrogen gas was flowed (filled)into the fourth-neck separable flask. In such a state, the suspensionwas reacted at a temperature of 70° C. for 5 hours. Thereafter, a firstcapsule layer constituted of the acryl-based resin was formed in thesuspension, and then pre-microcapsules encapsulating the dispersionliquid and the contact particles (carbon black) were obtained in thesuspension.

The thus obtained pre-microcapsules were cooled by a temperature of 25°C. Thereafter, coarse particles of the pre-microcapsules were removed bya standard sieve “a” having a sieve pore size of 32 μm.

A capsule dispersion liquid (suspension) of 1000 ml in which thepre-microcapsules were dispersed was added into a beaker of 2 L volume.The beaker was left to allow the pre-microcapsules to settle down in thecapsule dispersion liquid. Thereafter, the washing, the settling, andthe classifying operations were repeatedly carried out. These operations(a set of the washing, the settling, and the classifying operations)were repeated three times to wash the pre-microcapsules.

Next, all the pre-microcapsules were added into a separable flask havinga flat bottom and 500 ml volume, and deionized water was further addedinto the separable flask to set a total amount thereof to 200 g toobtain a seventh mixture. A temperature of the seventh mixture waselevated by 50° C. while stirring it.

Next, a solution of 100 g in which polyglycerol polyglycidyl ether of 15g, which is an epoxy compound (manufactured by Nagase ChemteXCorporation under the trade name of “DENACOL EX521”), was dissolved wasadded into the seventh mixture. After 30 minutes, a 5 wt %polyallylamine (of which weight-average molecular weight was 1000, andwhich manufactured by Nitto Boseki Co., Ltd. under the trade name of“Polyallylamine PAA-01”) solution of 50 g as a cross-linking agent wasadded into the seventh mixture drop by drop for 5 minutes.

A reaction was carried out at a temperature of 50° C. for 5 hours toprecipitate a charge applying shell on the surface of each of thepre-microcapsules (first capsule layer) and to thereby form a secondcapsule layer constituted of an epoxy-based resin. In this way,microcapsules were obtained. In each of the microcapsules, thedispersion liquid and the contact particles (carbon black) wereencapsulated in the capsule body which was constituted from the firstand second capsule layers.

In the second capsule layer formation step, it was determined that acolor of the second capsule layer was gradually changed to a blackcolor. In this regard, it is to be noted that the contact particlesincluded in the microcapsules were positively charged, the dispersionparticles included in the microcapsules were negatively charged, and thecapsule body was negatively charged.

Next, the thus obtained microcapsules were cooled by a temperature of25° C. as the pre-microcapsules described above. Then, coarse particlesof the microcapsules were removed by a standard sieve “a” having a sievepore size of 32 μm. Thereafter, the microcapsules were washed, and thenfine particles of the microcapsules were removed by a standard sieve “b”having a sieve pore size of 16 μm.

In other words, the microcapsules through the standard sieve “a” havingthe sieve pore size of 32 μm and not through the standard sieve “b”having the sieve pore size of 16 μm were collected. The black color ofthe microcapsules was maintained even after washing thereof.

A ratio of a solid portion included in a paste containing the thusobtained microcapsules was 65 wt %. This was defined as a microcapsulepaste (1).

Next, a solid matter constituted of butyl acrylate, 2-ethylhexylacrylate, methyl methacrylate, and hydroxyethyl methacrylate (of whichratio was 45:45:9:1) was prepared. Then, an emulsion of 13 g in which anamount of the solid matter was 50 wt % and water of 10 g were added intothe microcapsule paste (1) of 30 g to obtain a eighth mixture. Theeighth mixture was mixed by a mixer (manufactured by THINKY Corporationunder the trade name of “THINKY Mixer AR-100”) for 10 minutes to obtaina microcapsule coating material.

Next, the microcapsule coating material was applied onto secondelectrode, which was constituted of ITO, formed on a base substrate byusing an applicator. Thereafter, the applied microcapsule coatingmaterial was dried at a temperature of 90° C. for 10 minutes to form amicrocapsule-containing layer. In this way, a display sheet (1) wasobtained.

In this regard, it is to be noted that the microcapsule-containing layerwas not formed on the entire surface of the second electrode, that is,there were a part (conductive part) in which the microcapsule-containinglayer was not formed on the surface of the second electrode.

Next, a display device was manufactured by using the display sheet (1)as follows. In the thus obtained display sheet (1), the conductive partwas formed on the surface of the second electrode in a parallel state toone side thereof. The microcapsule-containing layer was formed on thesurface of the second electrode except for the surface on which theconductive part was formed.

That is, the microcapsule-containing layer was formed in a size of 5 cmlong and 3 cm short in a planner view. Such a display sheet (1) was usedfor manufacturing the display device.

A circuit board in which a first electrodes constituted of ITO wereformed on a base substrate was prepared. The circuit board was formed ina size 6 cm long and 4 cm short in a planner view and a thickness of 75μm. Such a display sheet (1) and such a circuit board were bondedtogether through an adhesive agent layer to obtain a laminate body.

At this time, arbitrary two parts of the display sheet (1) and thecircuit board were sealed with Sellotape (registered trademark).Thereafter, the laminate body was put on a glass board having athickness of 2 mm, and then passed through between two rolls of a rolllaminater to bond the display sheet (1) and the circuit board together.

The two rolls of the roll lamineter were made of a silicon rubber. Adiameter of each of two rolls was 3 inch, and a clearance between thetwo rolls was 0 mm. One roll (upper roll) of the two rolls was heated bya heat medium, and a temperature of the surface of the one roll was 120°C. The one roll was rotated by driving, and a position of the one rollwas fixed.

On the other hand, the other roll (lower roll) was not heated, androtated freely. The other roll was compressed to the one roll with anair pressure of 0.2 mPa.

The laminate body was arranged on the glass board so that themicrocapsule-containing layer included in the display sheet (1) wasopposite to the one roll (upper roll). A feeding rate of the laminatebody was 6 cm/min.

Examples 2 to 25 and Comparative Examples 1 to 12

In each of the Examples 2 to 25 and the Comparative Examples 1 to 12, adisplay device was manufactured in the same manner as in the Example 1except that the particles size (outer diameter) of each of themicrocapsules was adjusted by using standard sieves “a” and “b” as shownin Table 1.

In other words, in each of the Examples 2 to 25 and the ComparativeExamples 1 to 12, when a microcapsule coating material was produced,microcapsules through the standard sieve “a” shown in Table 1 and notthrough the standard sieve “b” shown in Table 1 were collected. Then,the collected microcapsules were used for manufacturing of the displaydevice.

TABLE 1 Standard Sieve “a” Standard Sieve “b” Comp. Ex. 1 16 μm — Comp.Ex. 2 26 μm 16 μm Ex. 1 32 μm 16 μm Ex. 2 38 μm 20 μm Ex. 3 38 μm 20 μmEx. 4 45 μm 26 μm Ex. 5 53 μm 32 μm Ex. 6 53 μm 32 μm Ex. 7 63 μm 38 μmEx. 8 75 μm 45 μm Comp. Ex. 3 90 μm 53 μm Comp. Ex. 4 100 μm  63 μmComp. Ex. 5 16 μm — Comp. Ex. 6 20 μm 16 μm Ex. 9 26 μm 20 μm Ex. 10 32μm 26 μm Ex. 11 32 μm 26 μm Ex. 12 38 μm 32 μm Ex. 13 45 μm 38 μm Ex. 1445 μm 38 μm Ex. 15 53 μm 45 μm Ex. 16 63 μm 53 μm Comp. Ex. 7 75 μm 63μm Comp. Ex. 8 90 μm 75 μm Ex. 17 45 μm 38 μm Ex. 18 45 μm 38 μm Ex. 1945 μm 32 μm Ex. 20 45 μm 32 μm Ex. 21 53 μm 32 μm Ex. 22 53 μm 32 μmComp. Ex. 9 53 μm 26 μm Comp. Ex. 10 53 μm 20 μm Comp. Ex. 11 60 μm 20μm Ex. 23 38 μm 26 μm Ex. 24 53 μm 38 μm Ex. 25 63 μm 45 μm Comp. Ex. 1275 μm 53 μm

2. Measurement of Charge Amount of Particles (Contact Particles andDispersion Particles)

Iron powder (manufactured by DOWA IP CREATION CO., LTD. under the tradename of “DSP-128”) of 20 g and the contact particles of 0.4 g were addedinto a vessel of 50 ml volume which was made of polypropyrene, and thenmixed for 5 minutes at an agitating number of 100 rpm by using a ballmill to obtain a mix powder.

A charge amount of the mix powder was measured by a blow-off typeapparatus for measuring charge amounts of powder (manufactured byTOSHIBA CHEMICAL CORPORATION under the trade name of “MODEL TB-200”).The result has been shown in Synthesis Example 1 described above. Thatis, the charge amount was +85 μc/g.

Furthermore, a charge amount of a mix powder including the dispersionparticles and iron powder was also measured in the same manner as themix powder including the iron powder and the contact particle. Theresult has been shown in Synthesis Example 1 described above. That is,the charge amount was −36 μc/g.

3. Measurement of CV Value

In each of the Examples 1 to 25 and the Comparative Examples 1 to 12, anaverage value (average capsule diameter) of outer diameters of themicrocapsules and a standard deviation of the outer diameters of themicrocapsules were measured and calculated by using a particle sizedistribution measurement apparatus (manufactured by Beckman Coulter,Inc. under the trade name of “Mdtisizer 3 type system”) and imageprocessed micrographs.

Then, a CV value (%) of the outer diameters of the microcapsules wascalculated by using the average capsule diameter and the standarddeviation. That is, the CV value was calculated the following formula:CV value (%)=standard deviation/average capsule diameter×100. Theresults were shown in Table 2.

4. Evaluation

In the display device obtained in each of the Examples 1 to 25 and theComparative Examples 1 to 12, a pulse voltage of 15 V and 400millisecond was applied to between the first electrodes and the secondelectrode to display a black color. A brightness of the black color wasmeasured by a reflection density meter (manufactured by X-RiteIncorporated. under the trade name of “SpectroEye”).

Next, a polarity of the applied voltage was switched reversely, and thena pulse voltage of 15 V and 400 millisecond was applied to between thefirst electrodes and the second electrode to display a white color. Abrightness of the white color was measured by the reflection densitymeter. Thereafter, display contrast was obtained (calculated) by usingthe brightnesses of the black color and the white color. The resultswere shown in Table 2.

TABLE 2 Average Capsule Standard CV White Black Diameter Deviation ValueColor Color Display (μm) (μm) (%) (%) (%) Contrast Comp. Ex. 1 14 2.618.6 31 8 3.9 Comp. Ex. 2 18 3.4 18.9 33 7 4.7 Ex. 1 22 4.3 19.5 33 5.95.6 Ex. 2 28 5.5 19.6 37 5.8 6.4 Ex. 3 31 6 19.4 37.5 5.3 7.1 Ex. 4 367.2 20.0 38.6 5 7.7 Ex. 5 40 7.6 19.0 41.3 4.8 8.6 Ex. 6 42 8.8 19.6 394.7 8.3 Ex. 7 51 9.7 19.0 37.5 5.4 6.9 Ex. 8 60 11.2 18.7 36 6.8 5.3Comp. Ex. 3 70 13.6 19.4 31 8 3.9 Comp. Ex. 4 80 15.4 19.3 26 10 2.6Comp. Ex. 5 15 1.3 8.7 32 7.5 4.3 Comp. Ex. 6 18 1.6 8.9 33 6.8 4.9 Ex.9 23 2.1 9.1 37.6 5.3 7.1 Ex. 10 28.5 2.8 9.8 41 4.9 8.4 Ex. 11 30 2.89.3 44.5 4.6 9.7 Ex. 12 35 3.5 10.0 46.8 4.6 10.2 Ex. 13 41 3.6 8.8 474.2 11.2 Ex. 14 43 3.8 8.3 43 4.4 9.8 Ex. 15 50 4.4 8.8 44 5.3 8.3 Ex.16 59 5.6 9.5 43 5.8 7.4 Comp. Ex. 7 72 6.3 8.8 38 8 4.8 Comp. Ex. 8 818 9.9 35 9 3.9 Ex. 17 43 3 7.0 46 3.9 11.8 Ex. 18 41 3.5 8.5 47.5 4.111.6 Ex. 19 42 5 11.9 45 4.3 10.5 Ex. 20 39 6 15.4 43 4.3 10.0 Ex. 21 407 17.5 42 5 8.4 Ex. 22 38 7 18.4 39 5.3 7.4 Comp. Ex. 9 42 9.8 23.3 316.2 5.0 Comp. Ex. 10 41 11.8 28.8 30 6.7 4.5 Comp. Ex. 11 39 13 33.3 288 3.5 Ex. 23 31 4.7 15.2 40 4.8 8.3 Ex. 24 45 7 15.6 43 4.6 9.3 Ex. 2550 7.2 14.4 42 5.6 7.5 Comp. Ex. 12 65 9.9 15.2 34 6.7 5.1

As shown in Table 2, the display contrast was high in the display deviceobtained in each of the Examples 1 to 25. In contrast, the displaycontrast was low in the display device obtained in each of theComparative Examples 1 to 12.

FIG. 20 is an electron microscope photograph of microcapsules when awhite color is displayed after a black color is displayed in the displaydevice obtained in Example 23. FIG. 21 is an electron microscopephotograph of microcapsules when a white color is displayed after ablack color is displayed in the display device obtained in ComparativeExample 10.

As shown in FIG. 20, in the microcapsules of the display device obtainedin the Example 23, colors of all of the microcapsules were a white colorwithout that parts of the surfaces of the microcapsules became a blackcolor. In contrast, as shown in FIG. 21, in the microcapsules of thedisplay device obtained in the Comparative Example 10, parts of thesurfaces of the microcapsules were the black color. That is, all of themicrocapsules were not the white color.

1. A display device comprising: a microcapsule-containing layerincluding a plurality of microcapsules each having an outer diameter,wherein a variation of the outer diameters of the plurality ofmicrocapsules can be defined by an average value and a CV value, andwherein each of the plurality of microcapsules comprised of: a shellhaving an inner surface; contact particles electrically charged andprovided within the shell in an contact state that the contact particlesare in contact with the inner surface of the shell, and the contactparticles having a hue; and a scattering body for scattering light, andthe scattering body provided within the shell; or a colored particleshaving a different hue from the hue of the contact particles, and thecolored particles provided within the shell; and a pair of electrodesthat when an electrical voltage is applied to between the pair ofelectrodes, electrical fields to act on the contact particles aregenerated; wherein the average value of the outer diameters of theplurality of microcapsules is in the range of 20 to 60 μm, and the CVvalue of the outer diameters of the microcapsules is 20% or less, andwherein in a case where the electrical voltage is applied to between thepair of electrodes, the contact particles are moved along the innersurface of the shell while maintaining the contact state with the innersurface of the shell.
 2. The display device as claimed in claim 1,wherein the contact particles are in contact with the inner surface ofthe shell due to an electrostatic force exerted therebetween.
 3. Thedisplay device as claimed in claim 1, wherein the contact particles havea polarity, the microcapsules have net charges having the same polarityas the polarity of the contact particles, and the net charges areexisted within the shell, so that the contact particles are in contactwith the inner surface of the shell due to the same polarity of the netcharges.
 4. The display device as claimed in claim 1, wherein a force ofholding the contact particles against the inner surface of the shell isgreater than an electrostatic force of acting on the contact particlesdue to the electrical fields generated between the pair of electrodes.5. The display device as claimed in claim 1, wherein the scattering bodyor the colored particles comprise a liquid filled in the shell.
 6. Thedisplay device as claimed in claim 5, wherein the liquid is constitutedof a liquid-phase dispersion medium and dispersion particles dispersedin the liquid-phase dispersion medium.
 7. The display device as claimedin claim 6, wherein the dispersion particles comprise particles ofscattering light or colored particles.
 8. The display device as claimedin claim 6, wherein the contact particles have a polarity, and thedispersion particles are not substantially electrically charged, or thedispersion particles are electrically charged in an opposite polarity asthe polarity of the contact particles.
 9. The display device as claimedin claim 1, wherein the scattering body or the colored particles is/area structural body provided within the shell so as to be spaced apartfrom the inner surface of the shell to a predetermined distance, and thestructural body having an outer surface, wherein the contact particlesare positioned between the inner surface of the shell and the outersurface of the structural body.
 10. The display device as claimed inclaim 1, wherein the display device has a side surface, and an averageroundness R of the microcapsules represented by the following formula(I) is in the range 0.88 to 1 when viewed from the side surface of thedisplay device,wherein R=L₀/L₁  (I), and wherein L₁ (μm) represents a circumference ofa projected image of the microcapsule that is a subject of measurement,and L₀ (μm) represents a circumference of a perfect circle having thesame area as that of the projected image of the microcapsule that is thesubject of measurement.
 11. The display device as claimed in claim 1,wherein the shell comprises a first layer and a second layer arrangedoutside the first layer, and each of the first layer and the secondlayer has a shell-like shape.
 12. The display device as claimed in claim1, wherein the display surface has a display surface, positions of thecontact particles included in the microcapsules are adjusted byadjusting of a magnitude of the electrical voltage to be applied tobetween the pair of electrodes and/or a time of applying the electricalvoltage to between the pair of electrodes, so that when the displaydevice is viewed from the display surface, a ratio of an area of aregion in which the contact particles provided within the shell areviewed and an area of a region in which the scattering body or thecolored particles provided within the shell is/are viewed is adjustable.13. A method of manufacturing a display device, comprising: amicrocapsule-containing layer formation step for forming amicrocapsule-containing layer including a plurality of microcapsuleseach having an outer diameter and a shell having an inner portion withan inner surface, the microcapsules each produced by encapsulating aplurality of electrically charged contact particles having a hue and apolarity, and a scattering body for scattering light or a coloredparticles for having a different hue from the hue of the contactparticles, wherein a CV value of the outer diameters of themicrocapsules is 20% or less; and an electrode formation step forforming a pair of electrodes that when an electrical voltage is appliedto between the pair of electrodes, electrical fields to act on thecontact particles are generated, wherein the microcapsule-containinglayer formation step comprises a charging step for providing netcharges, of which polarity is the same as the polarity of the contactparticles, to the inside of the shell after forming the inner portion orthe entirety of the shell, so that the contact particles are in contactwith the inner surface of the shell.
 14. The method as claimed in claim13, wherein the shell comprises a first layer corresponding to the innerportion and a second layer arranged outside the first layer, and each ofthe first layer and the second layer has a shell-like shape, and thecharging step is performed when forming the second layer.
 15. The methodas claimed in claim 13, wherein each of the microcapsules has an outersurface opposite to the side of the inner portion with the innersurface, wherein in the microcapsule-containing layer formation step,the microcapsule-containing layer is formed using a microcapsule coatingmaterial prepared by mixing the microcapsules with a fixing materialthat makes close contact with the outer surface of each of themicrocapsules to fix the microcapsules in place, and the charging stepis performed after the microcapsule-containing layer formation step. 16.An electronic apparatus provided with the display device defined byclaim 1.